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High-temperature microfluidic devices (such as gas chromatography microcolumns) have traditionally been fabricated using photolithography, etching, and wafer bonding which allow for precise microscale features but lack the ability to form complex 3D designs. Metal additive manufacturing could enable higher complexity microfluidic designs if reliable methods for fabrication are developed, but forming small negative features is challenging--especially in powder-based processes. In this paper, the formation of sealed metal microchannels was demonstrated using stainless-steel binder jetting with bronze infiltration. To create small negative features, bronze infiltrant must fill the porous part produced by binder jetting without filling the negative features. This was achieved through sacrificial powder infiltration (SPI), wherein sacrificial powder reservoirs (pore size ~60 µm) are used to control infiltrant pressure. With this pressure control, the infiltrant selectively filled the small pores between particles in the printed part (pore size ~3 µm) while leaving printed microchannels (700 µm and 930 µm) empty. To develop the SPI method, a pore filling study was performed in this stainless-steel/bronze system with 370 µm, 650 µm, and 930 µm microchannel segments. This study enabled SPI process design on these length scales by determining variations in pore filling across a sample and preferential filling between different sized pores. [ABSTRACT FROM AUTHOR]

An integrated optical isolator is a crucial part of photonic integrated circuits (PICs). Existing optical isolators, predominantly based on the silicon-on-insulator (SOI) platform, face challenges in integrating with active devices. We propose a broadband, compact TM mode Mach–Zehnder optical isolator based on InP-on-insulator platforms. We designed two distinct magneto-optical waveguide structures, employing different methods for bonding Ce:YIG and InP, namely O2 plasma surface activation direct wafer bonding and DVS-benzocyclobutene (BCB) adhesive bonding. Detailed calculations and optimizations were conducted to enhance their non-reciprocal phase shift (NRPS). At a wavelength of 1550 nm, the direct-bonded waveguide structure achieved a 30 dB bandwidth of 72 nm with a length difference of 0.256 µm. The effects of waveguide arm length, fabrication accuracy, and dimensional errors on the device performance are discussed. Additionally, manufacturing tolerances for three types of lithographic processes were calculated, serving as references for practical manufacturing purposes. [ABSTRACT FROM AUTHOR]

Bodies made from elastically stiff material usually bind very weakly unless the surfaces are flat and extremely smooth. In direct wafer bonding flat surfaces bind by capillary bridges and by the van der Waals interaction, which act between all solid objects. Here we study the dependency of the work of adhesion on the humidity and surface roughness in hydrophilic direct wafer bonding. We show that the long-wavelength roughness (usually denoted waviness) has a negligible influence on the strength of wafer bonding (the work of adhesion) from the menisci that form from capillary condensation of water vapor. AFM surface topography for Si(100) wafer [ABSTRACT FROM AUTHOR]

A new technique is assessed in order to measure, at the wafer scale, direct bonding energies. It is derived from the standard Double Cantilever Beam (DCB) method and uses interferometry in confocal IR laser source microscopy to measure crack openings. Such a bonding energy measurement protocol has better accuracy compared to other techniques. This is due to a better confocal microscopy resolution and the high intensity of the laser source. The elastic energy stored in bent wafers is obtained by measuring the beam curvature. DCB deformation models are discussed from the short-range crack opening theory to long distance beam-bending theories. Comparison is made between models, experimental results, and FEM simulations. Finally, the bonding energy error during standard measurements is estimated. [ABSTRACT FROM AUTHOR]

Room temperature wafer bonding is a desirable approach for the packaging and assembly of diverse electronic devices. The formation of SiO 2 layer at the bonding interface is crucial for a reliable wafer bonding as represented by conventional bonding techniques such as hydrophilic bonding and glass frit bonding. This paper reports a novel concept of room temperature wafer bonding based on the conversion of polysilazane to SiO 2 at the bonding interface. As polysilazane is converted to SiO 2 by hydrolysis, in this work, adsorbed water is introduced to the bonding interface by plasma treatment, thereby facilitating the formation of SiO 2 at the wafer bonding interface. The experimental results indicate that the adsorbed water from the plasma treatment diffuses into the polysilazane layer and facilitates its hydrolysis and conversion. The proposed method demonstrates the successful wafer bonding at room temperature with high bond strength without interfacial voids. This technique will provide a new approach of bonding wafers at room temperature for electronics packaging. [ABSTRACT FROM AUTHOR]

Purpose: Wafer bonding is a key process for 3 D advanced packaging of integrated circuits. It requires very high accuracy for the wafer alignment. To solve the problems of large movement stroke, position calibration error and low production efficiency in optical alignment, this paper aims to propose a new wafer magnetic alignment technology (MAT) which is based on tunnel magneto resistance effect. MAT can realize micro distance alignment and reduces the design and manufacturing difficulty of wafer bonding equipment. Design/methodology/approach: The current methods and existing problems of wafer optical alignment are introduced, and the mechanism and realization process of wafer magnetic alignment are proposed. Micro magnetic column (MMC) marks are designed on the wafer by the semiconductor manufacturing process. The mathematical model of the space magnetic field of the MMC is established, and the magnetic field distribution of the MMC alignment is numerically simulated and visualized. The relationship between the alignment accuracy and the MMC diameter, MMC remanence, MMC thickness and sensor measurement height was studied. Findings: The simulation analysis shows that the overlapping double MMCs can align the wafer with accuracy within 1 µm and can control the bonding distance within the micrometer range to improve the alignment efficiency. Originality/value: Magnetic alignment technology provides a new idea for wafer bonding alignment, which is expected to improve the accuracy and efficiency of wafer bonding. [ABSTRACT FROM AUTHOR]

This work investigates substrate leakage in Capacitive Micromachined Ultrasonic Transducers, (CMUTs) having thin backings. CMUTs produced with solid or rigid substrates have a high Q resonance with flat baseline. However, if the operating wavelength of CMUT becomes larger than the thickness of substrate the real part of cell impedance shows elevated baselines with more leakage at DC than at higher frequencies. When a clamped CMUT membrane is excited harmonically the vibrations produced are counterbalanced by the backing medium. Hence some of the energy is coupled to substrate as loss resulting in a lower mechanical Q of resonance. We first derive this energy coupled to the backing medium using FEA analysis considering the velocity field and associated tensile stresses in a thin backing. Substrate impedance is found numerically from isotropic damping of dispersive elastic waves in the backing. This backing impedance is introduced as a shunt mechanical loss across the transduction force in equivalent circuit model. We characterize the measured impedance of CMUT cells with both FEMs and linear circuit models. Simulations results closely agree with the measured impedance levels, frequency and bandwidth of resonance. [ABSTRACT FROM AUTHOR]

Ambient mass spectrometry imaging (MSI) is a powerful technique that allows for the simultaneous mapping of hundreds of molecules in biological samples under atmospheric conditions, requiring minimal sample preparation. We have developed nanospray desorption electrospray ionization (nano-DESI), a liquid extraction-based ambient ionization technique, which has proven to be sensitive and capable of achieving high spatial resolution. We have previously described an integrated microfluidic probe, which simplifies the nano-DESI setup, but is quite difficult to fabricate. Herein, we introduce a facile and scalable strategy for fabricating microfluidic devices for nano-DESI MSI applications. Our approach involves the use of selective laser-assisted etching (SLE) of fused silica to create a monolithic microfluidic probe (SLE-MFP). Unlike the traditional photolithography-based fabrication, SLE eliminates the need for the wafer bonding process and allows for automated, scalable fabrication of the probe. The chamfered design of the sampling port and ESI emitter significantly reduces the amount of polishing required to fine-tune the probe thereby streamlining and simplifying the fabrication process. We have also examined the performance of a V-shaped probe, in which only the sampling port is fabricated using SLE technology. The V-shaped design of the probe is easy to fabricate and provides an opportunity to independently optimize the size and shape of the electrospray emitter. We have evaluated the performance of SLE-MFP by imaging mouse tissue sections. Our results demonstrate that SLE technology enables the fabrication of robust monolithic microfluidic probes for MSI experiments. This development expands the capabilities of nano-DESI MSI and makes the technique more accessible to the broader scientific community. [ABSTRACT FROM AUTHOR]

The paper presents an analytical model for the design of a composite membrane circular capacitive micromachined ultrasonic transducers (cMUT) cell. The analytical model harnesses composite membrane layer cMUT cell based on the mass-spring-damper system. The effects of damping due to the surrounding medium and acoustic impedance of self-radiation as well as identical neighbouring cells cluster are also modelled for dynamic analysis of unit cMUT cell. The validation of analytically obtained results is performed through FEM simulations using MEMSCAD tool CoventorWare®. The analytically obtained results show good agreement with the FEM simulation results. The designed structure is based on the wafer bonding technology, which is well established at the authors' laboratory. It is a low temperature anodic bonding process without through silicon via/through glass via (TSV/TGV) technique requirement (Aditi et al. in IEEE 24th Electronics Packaging Technology Conference (EPTC), 2022). Composite membrane circular cMUT cell is designed and validated for air-coupled application; moreover, the model developed is also applicable to other fluids as well. [ABSTRACT FROM AUTHOR]

Detecting mechanical fatigue of metallic components is always a challenge in industries. In this work, we proposed to monitor the low-cycle fatigue of a 6061 aluminum alloy based on internal friction (IF) measurement, which is realized by a quantitative electromechanical impedance (Q-EMI) method using a small piezoelectric wafer bonded on the specimen. Large stress amplitude (230 MPa) was employed in the testing; thus, the fatigue life can always be below 105 cycles. It was found that except for the initial testing stage, the IF always increases steadily with the increasing fatigue cycles. Before the fatigue failure, the IF can reach 2.5–3.4 times the initial value, which is thought to be caused by the micro-cracks forming and growing. In comparison, the resonance frequency of the specimen just drops by about 2% compared with the initial value. Finally, a fatigue criterion based on IF measurement is suggested for aluminum alloys and it can also be extended to other metals. [ABSTRACT FROM AUTHOR]

We demonstrate a controllable depletion of the nitrogen buffer gas pressure in a micro-machined cesium (Cs) vapor cell from the dynamic heating of an alkali dispenser pill. When the alkali source is laser activated, the gettering compounds within the alkali pill dispenser reduce the nitrogen (N2) content from the vapor for fine-tuning of the alkali to buffer gas pressure ratio, with a demonstrated pressure step size as low as 1 Torr. Additionally, we decrease the buffer gas pressure below 100 mTorr to evaluate the presence of other potential broadening mechanisms. Real-time control of the gas pressure ratio in the vapor cell will have notable benefits for refining atomic sensor performance and provide a routine to achieve various target pressures across a wafer bonded with a uniform back-filled buffer gas pressure. [ABSTRACT FROM AUTHOR]

Wafer warpage affects the resolution of photolithography, process alignment, and wafer bonding, which leads to the degradation of the device’s yield, performance, and reliability. With the development of devices, the increase of metal layers in the stack direction will worsen the warpage problem. We investigate the Wafer-to-Wafer (W2W) bonding process-induced warpage issue with experiments and a full wafer simulation. A concave wafer warpage of $70~\mu \text{m}$ is observed for a single wafer with a $7.8~\mu \text{m}$ thickness DRAM layer due to the shrinkage of the DRAM layer. In both experiments and simulation, we reveal that the W2W bonding process induces warpage 3 times the single wafer warpage value, as the deformation restriction of the DRAM layers by the thinned Si layer is weak. Furthermore, good agreement is observed between the simulated results and the measured data, which validates the simulation mode. We estimate the wafer warpage of the multi-stack wafer bonding with the validated model. As an example, the warpage of a 4-stack wafer is revealed to be 7 times the single wafer warpage value. This study provides useful information on wafer warpage in the W2W bonding process and reveals the severe warpage issue with increasing the stacked metal layers. [ABSTRACT FROM AUTHOR]

Glass has unique properties that make it attractive for many applications. Combining glass with Si fabrication process would create new possibilities not only in device performance and form factor, but also scale economies. Key challenges in using glass wafers in a Si fab include lack of opacity and electrical conductivity as well as metallic and particle contamination. These challenges can be overcome through a suitable coating on the glass wafer and rigorous particle removal throughput the fabrication and use process. For applications that demand high precision to support direct wafer bonding and lithography, glass wafers can be engineered to deliver the required surface smoothness and flatness. [ABSTRACT FROM AUTHOR]

The development of big data and artificial intelligence technology is increasing the need for electronic devices to become smaller, cheaper, and more energy efficient, while also having enhanced functionalities. However, the miniaturization of silicon chip technology is approaching its Moore's law (i.e., physical) limits. Thus, the application of three-dimensional integrated circuits (3D ICs), in which multiple chips are stacked vertically, provides the most achievable approach for the advancement of post-Moore electronics. In the recent decade, various key techniques have been developed for stacking chips vertically such as through-silicon vias, micro-bumps, low melting point tin–bismuth solders, redistribution layers, and copper-to-copper direct bonding. However, the need for high current densities in these structures results in severe Joule heating, making electromigration (EM) an increasingly challenging problem. This paper reviews studies on EM failures, mechanisms, and potential solutions for the key components of 3D IC packaging. [ABSTRACT FROM AUTHOR]

Small-pitch 3D pixel sensors have been developed to equip the innermost layers of the ATLAS and CMS tracker upgrades at the High Luminosity LHC. They feature 50 × 50 and 25 × 100 μ m 2 geometries and are fabricated on p-type Si–Si Direct Wafer Bonded substrates of 150 μ m active thickness with a single-sided process. Due to the short inter-electrode distance, charge trapping effects are strongly mitigated, making these sensors extremely radiation hard. Results from beam test measurements of 3D pixel modules irradiated at large fluences ( 10 16 n e q / cm 2 ) indeed demonstrated high efficiency at maximum bias voltages of the order of 150 V. However, the downscaled sensor structure also lends itself to high electric fields as the bias voltage is increased, meaning that premature electrical breakdown due to impact ionization is a concern. In this study, TCAD simulations incorporating advanced surface and bulk damage models are used to investigate the leakage current and breakdown behavior of these sensors. Simulations are compared with measured characteristics of 3D diodes irradiated with neutrons at fluences up to 1.5 × 10 16 n e q / cm 2 . The dependence of the breakdown voltage on geometrical parameters (e.g., the n + column radius and the gap between the n + column tip and the highly doped p + + handle wafer) is also discussed for optimization purposes. [ABSTRACT FROM AUTHOR]

Graphene is a promising candidate for future electronic applications. Manufacturing graphene-based electronic devices typically requires graphene transfer from its growth substrate to another desired substrate. This key step for device integration must be applicable at the wafer level and meet the stringent requirements of semiconductor fabrication lines. In this work, wet and semidry transfer (i.e. wafer bonding) are evaluated regarding wafer scalability, handling, potential for automation, yield, contamination, and electrical performance. A wafer scale tool is developed to transfer graphene from 150 mm copper foils to 200 mm silicon wafers without adhesive intermediate polymers. The transferred graphene coverage ranges from 97.9 % to 99.2 % for wet transfer and from 17.2 % to 90.8 % for semidry transfer, with average copper contaminations of 4.7 × 1013 (wet) and 8.2 × 1012 atoms/cm2 (semidry). The corresponding electrical sheet resistance extracted from terahertz timedomain spectroscopy varied from 450 to 550 O sq-1 for wet transfer and from 1000 to 1650 O sq-1 for semidry transfer. Although the wet transfer is superior in terms of yield, carbon contamination level, and electrical quality, wafer bonding yields lower copper contamination levels and provides scalability due to existing industrial tools and processes. Our conclusions can be generalized to all 2D materials. [ABSTRACT FROM AUTHOR]

Germanium-on-insulator (GeOI) films fabricated using the Smart Cut™ wafer bonding and film exfoliation technology were investigated for the mechanical properties and induced phase transformations by using nanoindentation and Raman spectroscopy experiments. The hardness and modulus results of the GeOI films are significantly different from the literature published Silicon-on-Insulator and bulk germanium results. The GeOI films are softer and more flexible as compared to bulk Ge hardness and stiffness properties. The Raman spectroscopy of the spherical indents indicates bands of metastable Ge phases @ 220 cm−1, 195 cm−1, and 184 cm−1 wavenumbers. Our results demonstrate that a spherical indenter impacted a wider area of contact and produced GeOI indented surfaces free of cracks and fracture. The spherical indenter tip kept the Ge top layer intact when compared to the Berkovich indenter tip during penetration. In contrast, the Berkovich indenter tip developed excessive fracture that resulted in displacing the Ge top layer sideways and exposed the Si substrate underneath revealing Raman spectra bands of metastable Si phases @ 350 cm−1, 399 cm−1, and 430 cm−1. [ABSTRACT FROM AUTHOR]

Dark current characteristics of germanium (Ge) vertical p-i-n photodetectors were studied. Ge photodetectors were demonstrated on the germanium-on-insulator (GOI) platforms realized via direct wafer bonding and layer transfer. GOI platforms with two different threading dislocation densities (TDDs) of 3.2 × 106 cm−2 (low TDD) and 5.2 × 108 cm−2 (high TDD) were varied via furnace annealing in oxygen ambient. An ultra-low dark current density of 1.12 mA/cm2 for epi-Ge photodetectors was obtained for a low TDD Ge photodetector. This is reduced by a factor of 53 in comparison with a high TDD Ge photodetector. A dominant leakage contribution component shifts from bulk leakage to surface leakage as TDD decreases to 3.2 × 106 cm−2, suggesting that advanced surface passivation is required to further reduce the leakage current. Through an activation energy study, it is revealed that a primary bulk leakage mechanism shifts from Shockley–Read–Hall (SRH) leakage to diffusion leakage in a temperature range of 323–353 K. The surface leakage performed with plasma enhanced chemical vapor deposition-deposited SiO2 is governed by SRH and trap-assisted tunneling leakage processes. Two orders of magnitude enhancement in the effective carrier lifetime is observed with the reduction in TDD. This work suggests that bulk leakage current density and effective lifetime analysis provide a better understanding of TDD-dependent dark leakage current study. [ABSTRACT FROM AUTHOR]

In this study, room-temperature wafer bonding of Al2O3 thin films on Si thermal oxide wafers, which were deposited using atomic layer deposition (ALD), was realized using the surface-activated bonding (SAB) method. Transmission electron microscopy (TEM) observations indicated that these room-temperature-bonded Al2O3 thin films appeared to work well as nanoadhesives that formed strong bond between thermally oxidized Si films. The perfect dicing of the bonded wafer into dimensions of 0.5 mm × 0.5 mm was successful, and the surface energy, which is indicative of the bond strength, was estimated to be approximately 1.5 J/m2. These results indicate that strong bonds can be formed, which may be sufficient for device applications. In addition, the applicability of different Al2O3 microstructures in the SAB method was investigated, and the effectiveness of applying ALD Al2O3 was experimentally verified. This successful SAB of Al2O3 thin films, which is a promising insulator material, opens the possibility of future room-temperature heterogenous integration and wafer-level packaging. [ABSTRACT FROM AUTHOR]

Mark's precise positioning is critical for achieving wafer bonding accuracy. A Mark positioning algorithm is proposed to improve the accuracy and stability of Mark positioning. Shape template matching can effectively reduce the impact of image quality on positioning accuracy, but it can only achieve pixel precision Mark location. On the basis of this method, the algorithm uses the facet model method to extract the sub-pixel edge information for the Mark contour, and combines the sub-pixel traversal strategy to achieve accurate sub-pixel precision Mark location. Simultaneously, the composite template method is proposed for the first time to improve the template information's quality, which effectively improves the robustness of the algorithm to image quality. The simulation results indicate that the algorithm is capable of positioning with an accuracy of approximately 0.04 pixels. The experimental results indicate that the algorithm is capable of positioning with an accuracy of approximately 0.052 pixels and is resistant to image noise and blur, which meets the accuracy and stability requirements for Mark positioning in wafer bonding alignment. • A Mark positioning algorithm based on sub-pixel shape template matching is proposed that enables high-precision mark location during wafer bonding alignment. • The facet model method is used to introduce sub-pixel edge point information for shape template matching, and the sub-pixel positioning is realized combined with the search strategy of sub-pixel step size. • The composite template method is proposed to improve the template quality, which finally improves the reliability of template matching. • Simulation and experiments demonstrate that the algorithm has high positioning accuracy and robustness to image quality. [ABSTRACT FROM AUTHOR]

Anodic bonding is a reliable packaging method for MEMS devices, and the surface properties of the wafer directly affect the bonding efficiency. Therefore, the surface treatment of the wafer to be bonded is necessary. Herein, the effects of three different surface cleaning processes (degreasing, piranha solution and RCA solution) on the wafer surface were investigated by atomic force microscopy, scanning electron microscopy, infrared spectroscopy, and anodic bonding experiments. The analysis showed that during the anodic bonding of the RCA solution-cleaned wafer and Pyrex glass, the bonding interface was more closely attached, and the best surface properties were obtained. The anodic bonding experiments of the wafer and Pyrex glass showed that the bonding current increased with the applied voltage, and the bonding time decreased accordingly. This was most evident in the case of RCA cleaning. The SEM images showed that as the bonding voltage increased, the bonding interface became more uniform without obvious voids. Due to the influence of the strong electric field and temperature field, an irreversible chemical reaction occurred at the bonding interface, which formed a bonding layer that was key to successful bonding. [ABSTRACT FROM AUTHOR]

Thin-film lithium niobate (TFLN) photonic integrated circuits (PICs) have emerged as a promising integrated photonics platform for the optical communication, microwave photonics, and sensing applications. In recent years, rapid progress has been made on the development of low-loss TFLN waveguides, high-speed modulators, and various passive components. However, the integration of laser sources on the TFLN photonics platform is still one of the main hurdles in the path toward fully integrated TFLN PICs. Here, we present the heterogeneous integration of InP-based semiconductor lasers on a TFLN PIC. The III–V epitaxial layer stack is adhesively bonded to a TFLN waveguide circuit. In the laser device, the light is coupled from the III–V gain section to the TFLN waveguide via a multi-section spot size converter. A waveguide-coupled output power above 1 mW is achieved for the device operating at room temperature. This heterogeneous integration approach can also be used to realize on-chip photodetectors based on the same epitaxial layer stack and the same process flow, thereby enabling large-volume, low-cost manufacturing of fully integrated III–V-on-lithium niobate systems for next-generation high-capacity communication applications. [ABSTRACT FROM AUTHOR]

The electro-mechanical impedance (EMI) method has been demonstrated to be a powerful tool to detect the small local damages in various engineering structures, due to its high-frequency vibration characteristics. However, this technique is difficult to accurately determine the degree and location of structural damages. In this paper, an inverse analysis combining the measured EMI signatures and the Transfer Matrix Method (TMM) is proposed to identify the damages in the steel rods. A milled groove is introduced into each steel specimen to simulate the local damage. By measuring the EMI signatures of the piezoelectric wafers bonded symmetrically on the upper and lower surfaces of the rectangular specimens respectively, the damage can be detected clearly, as well as natural frequencies being extracted in the relatively lower frequency range. The damage sizes and locations are further determined by connecting the frequency equations and any two measured natural frequencies. Tests on three samples show both damage sizes and locations are accurately detected, which indicates that the present method is quite feasible and effective for damage identification in the bar-type structures. [ABSTRACT FROM AUTHOR]

Self-calibration capabilities for flexible pressure sensors are greatly needed for fluid dynamic analysis, structure health monitoring and wearable sensing applications to compensate, in situ and in real time, for sensor drifts, nonlinearity effects, and hysteresis. Currently, very few self-calibrating pressure sensors can be found in the literature, let alone in flexible formats. This paper presents a flexible self-calibrating pressure sensor fabricated from a silicon-on-insulator wafer and bonded on a polyimide substrate. The sensor chip is made of four piezoresistors arranged in a Wheatstone bridge configuration on a pressure-sensitive membrane, integrated with a gold thin film-based reference cavity heater, and two thermistors. With a liquid-to-vapor thermopneumatic actuation system, the sensor can create precise in-cavity pressure for self-calibration. Compared with the previous work related to the single-phase air-only counterpart, testing of this two-phase sensor demonstrated that adding the water liquid-to-vapor phase change can improve the effective range of self-calibration from 3 psi to 9.5 psi without increasing the power consumption of the cavity micro-heater. The calibration time can be further improved to a few seconds with a pulsed heating power. [ABSTRACT FROM AUTHOR]

We propose and demonstrate an efficient grating coupler for integrated SiGe photonic devices. A bottom metal layer is adopted to enhance the coupling efficiency on the wafer backside. A low coupling loss of −1.34 dB and −0.79 dB can be theoretically obtained with optimal parameters for uniform and apodized grating couplers, respectively. The fabrication process is CMOS compatible without need of wafer bonding. The influence of fabrication errors on the coupling efficiency is analyzed in terms of substrate thickness, grating dimension and material refractive index. The results indicate a large tolerance for the deviations in practical fabrication. The measured coupling loss of the uniform grating is −2.7 dB at approximately 1465 nm with a 3 dB bandwidth of more than 40 nm. The proposed grating coupler provides a promising approach to realize efficient chip-fiber coupling for the SiGe photonic integration. [ABSTRACT FROM AUTHOR]

InGaSb-on-insulator (InGaSb-OI) and InAs/InGaAs/InAs-on-insulator (InAs/InGaAs-OI) structures have been realized on Si by a direct wafer bonding (DWB) technology using atomic-layer-deposition Al2O3. While strain introduced in InGaSb channel layers grown on InAs can enhance the hole mobility of the Sb-based channel layers, a difficult issue of fabricating InGaSb-OI wafers is to obtain a smooth InGaSb surface, which is mandatory for wafer bonding. In this study, the surface of a 20-nm-thick In0.185Ga0.815Sb channel grown on an InAs (100) substrate and an InAs (2.5 nm)/In0.185Ga0.815Sb (20 nm)/InAs (2.5 nm) channel with a 20-nm-thick GaSb buffer layer grown on an InAs (100) substrate by metal-organic chemical vapor deposition have a root mean square of the surface roughness as low as 0.16 and 0.22 nm, respectively, over a scan area of 10 × 10 μm2, which are smooth enough to employ the wafer bonding. As a result, the fabrication of the InGaSb-OI wafers by the DWB and the operation of InGaSb-OI p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) by using the DWB wafers are demonstrated. Also, the performance of InGaSb-OI p-MOSFETs is found to be improved by inserting ultrathin InAs layers between InGaSb and insulating buried oxide layers. An InGaSb-OI and an InAs/InGaAs-OI p-MOSFET under the accumulation-mode operation exhibit a peak mobility of ∼161 and ∼273 cm2/V s, respectively. The channel hole mobility of the InGaSb-OI p-MOSFET is higher than that of the GaSb-on-insulator (GaSb-OI) p-MOSFET and can exceed that of Si p-MOSFETs. [ABSTRACT FROM AUTHOR]

To meet the stringent requirements of 5G communication, we proposed a high-performance bulk acoustic wave (BAW) filter based on single crystal AlN piezoelectric films on a SiC substrate. The fabrication of the BAW filter is compatible with the GaN high electron mobility transistor (HEMT) process, enabling the implementation of the integration of the BAW device and high-performance monolithic microwave integrated circuit (MMIC). The single crystal AlN piezoelectric film with 650-nm thickness was epitaxially grown on the SiC substrate by Metal Organic Chemical Vapor Deposition (MOCVD). After wafer bonding and substrate removal, the single crystal AlN film with electrode layers was transferred to another SiC wafer to form an air gap type BAW. Testing results showed that the fabricated resonators have a maximum Q-factor up to 837 at 3.3 GHz resonant frequency and electromechanical coupling coefficient up to 7.2%. Ladder-type filters were developed to verify the capabilities of the BAW and process, which has a center frequency of 3.38 GHz with 160 MHz 3 dB bandwidth. The filter achieved a minimum 1.5 dB insertion loss and more than 31 dB out-of-band rejection. The high performance of the filters is attributed to the high crystallinity and low defects of epitaxial single crystal AlN films. [ABSTRACT FROM AUTHOR]

A sandwich structure, which is stacked by a wafer-level copper–copper (Cu–Cu) thermocompression bonding and a silicon–silicon (Si–Si) direct bonding, has been investigated for potential application as a hermetic seal in 3-D microsystem packaging. First, the bottom and middle layers are prebonded by hydrophilic Si direct bonding. Oxygen plasma is employed for surface activation. Then, the prebonded wafers and the top wafer are bonded via Cu thermocompression bonding at a bonding temperature of 300 °C and a bonding force of 8000 mbar for a duration of 1 h. The entire bonding process of the three layers has borne only one heating procedure, which could effectively reduce the residual stress after bonding. Cavities are etched to a volume of $21.4\times 10^{-3}$ cm3 following the MIL-STD-883E standard prescribed for microelectronics packaging. The helium leak test demonstrates that 96.8% of the samples present a superior leak rate smaller than $1.7\times 10^{-8}$ atm $\cdot $ cm3/s. Moreover, the interfacial adhesion energy between the Cu–Cu bonding interface and the Si–Si bonding interface was projected at 16.4 ± 4.6 J/ $\text{m}^{2}$ and Si breakage energy. The results hold great promise for 3-D microsystem wafer-level packaging. [ABSTRACT FROM AUTHOR]

In this work, the impact of plasma treatment on Si wafers with native oxide on top was systematically investigated using spectroscopic ellipsometry. A general applicable three-layer optical model structure for ellipsometry data fitting was developed and employed on samples treated with the N2, O2, and N2/O2 mixture plasma. Oxide-growth, amorphization of crystalline Si, and the formation of a transition layer between the SiO2 and the amorphous Si were detected. The estimated thicknesses of produced layers were confirmed by complementary methods, which allow precise ultra-thin layers thicknesses detection, namely, angle-resolved x-ray photoelectron spectroscopy and transmission electron microscopy. The depth-resolved chemical composition and the direct thickness measurements of the produced amorphous structure revealed pronounced elemental gradients and the absence of sharp interfaces. Nitrogen gas used in the plasma process was found to be implanted mainly at the interface of the SiO2/transition layer in the form of Si3N4. However, it was verified that it is feasible to employ one general ellipsometry model consisting of SiO2/transition layer/amorphous Si on crystalline Si for all plasma species due to comparably low Si3N4 concentrations as well as its refractive index n and absorption k similarity to SiO2. Spectroscopic ellipsometry is nondestructive and can be efficiently applied to analyze whole wafers without any sample preparation. It can be concluded that the present approach to ellipsometry model development and verification is well suited for plasma-activated direct wafer bonding processes. [ABSTRACT FROM AUTHOR]

This paper introduces a 3-D fused quartz dual-shell microstructure, discussing its design, simulation, fabrication, and instrumentation as a Microelectromechanical System (MEMS) gyroscope. The dual-shell was realized from plastic deformation of fused quartz using triple-stack wafer bonding and high-temperature micro-glassblowing processes. The fabrication process was developed and dual-shell prototypes with different design parameters were fabricated. A Finite Element (FE) model was presented to simulate the deformation of viscous fused quartz during the micro-glassblowing process. The model was utilized to predict the final 3-D geometry from the design process parameters. A modeling framework based on FE simulations was presented for designing the resonators as well as predicting the resonator’s response to transient excitation, such as shock and vibrations. Fused quartz dual-shell resonator prototype with Q-factors as high as 1.83 million and amplitude ringdown time of 120 seconds was demonstrated. An electrode substrate was designed and integrated with the dual-shell resonator for electrostatic excitation and detection of the vibration modes, as well as 3-D packaging and vacuum encapsulation of the sensing element. An open-loop angular rate gyro operation with electrostatic excitation and capacitive detection was demonstrated on the dual-shell resonator. The Allan deviation of zero rate output bias revealed Angle Random Walk (ARW) of $0.058 \deg /\sqrt {hr}$ and in-run bias instability of $0.4 \deg /hr$ without temperature control on the dual-shell resonator gyroscope. The proposed structure can be instrumented to operate as a resonator, a gyroscope, or other vibratory sensors, and is anticipated to have advantages for precision operation in a harsh environment. [ABSTRACT FROM AUTHOR]

We explore compatibility of Ru with Al-Ge eutectic wafer bonding. We first present experiments to check for the presence of Ru ternary alloy poisoning inhibiting Al-Ge melting as well as evaluations of Al-Ge melt wettability on Ru and diffusion outcomes following bond-simulating anneals. Results show that Ru is stable with no observed microstructural changes or dissolution in the melt, indicating no ternary poisoning for the applied thermal budget. Ru was found to act as an effective barrier offering good melt wettability in all considered configurations with Al and Ge. From inspection of the binary constituents of Al-Ge-Ru we propose that Al-Ge eutectic melting temperature will decrease marginally for Ru contamination in a 1-2% range before a drastic increase in melting temperature (>10°C/% Ru) at higher Ru compositions. We then demonstrate wafer-level packaged 200 mm devices and MEMS with strong bond outcomes of devices bearing Ru contacts. We conclude that Ru has high compatibility with Al-Ge eutectic bonding. [2022-0037] [ABSTRACT FROM AUTHOR]

Efficient use of incident sunlight is an important key issue for the improvement of solar cell performance. Here, we propose and experimentally demonstrate photon upconversion material mediated semiconductor bonding as a concept of interfacial functionalization. Our wavelength-converting semiconductor interface comprises rare earth doped upconversion nanoparticles embedded in a hydrogel matrix. Advantageously, the bonding process is conducted at room temperature in ambient air. As a proof of principle, photocurrent enhancement in bonded Si solar cells is demonstrated. Our technical scheme could be useful to improve the performance and structural flexibility of various optoelectronic devices by delivering the preferred frequency to each of the optical components. [ABSTRACT FROM AUTHOR]

Attachment of biorecognition molecules prior to microfluidic packaging is advantageous for many silicon biosensor-based lab-on-a-chip (LOC) devices. This necessitates biocompatible bonding of the microfluidic cartridge, which, due to thermal or chemical incompatibility, excludes standard microfabrication bonding techniques. Here, we demonstrate a novel processing approach for a commercially available, two-step curable polymer to obtain biocompatible ultraviolet initiated (UVA)-bonding of polymer microfluidics to silicon biosensors. Biocompatibility is assessed by UVA-bonding to antibody-functionalized ring resonator sensors and performing antigen capture assays while optically monitoring the sensor response. The assessments indicate normal biological function of the antibodies after UVA-bonding with selective binding to the target antigen. The bonding strength between polymer and silicon chips (non-biofunctionalized and biofunctionalized) is determined in terms of static liquid pressure. Polymer microfluidic cartridges are stored for more than 18 weeks between cartridge molding and cartridge-to-silicon bonding. All bonded devices withstand more than 2500 mbar pressure, far exceeding the typical requirements for LOC applications, while they may also be de-bonded after use. We suggest that these characteristics arise from bonding mainly through intermolecular forces, with a large extent of hydrogen bonds. Dimensional fidelity assessed by microscopy imaging shows less than 2% shrinkage through the molding process and the water contact angle is approximately 80°. As there is generally little absorption of UVA light (365 nm) in proteins and nucleic acids, this UVA-bonding procedure should be applicable for packaging a wide variety of biosensors into LOC systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Innovatively employed first-principles calculations to analyze the atomic-level bonding principles of heterogeneous wafer bonding interfaces. • Combines molecular dynamics and reaction kinetics for a multidisciplinary approach. • Presents eight interface models to explore bonding mechanisms. • Investigated annealing and oxygen plasma activation effects for optimizing bonding processes in optoelectronic integration. The direct bonding mechanism of Si/InP is systematically investigated using first-principles calculations. Charge density analysis reveals that Si can be bonded with either In or P and is polar covalent. The single Si-P bond is stronger than the Si-In bond and has a shorter bond length, the Si-P bond length is 2.356 Å compared to 2.590 Å for the Si-In ones, as it involves the sharing of electron pairs and a large transfer and redistribution of electrons. Notably, molecular dynamics simulations show that the interfacial strength of Si bonded to In is greater at room temperature. This is because, after sufficient relaxation, although the average strength of the Si-P bonds is still greater than that of Si-In, the number of Si-In bonds is approximately four times that of the Si-P bonds. The radial distribution function of the atoms in the interfacial layer further confirms that the terminal interface is stronger than the P-terminal interface. Appropriate annealing treatment can effectively increase the number and strength of bonds at the interface. Finally, the bonding mechanism of the oxygen plasma activation is studied using reaction kinetics. These findings contribute to the precise control and optimization of bonding processes, ultimately improving the reliability of optoelectronic integration. [ABSTRACT FROM AUTHOR]

We report a low-temperature and low-cost wafer-bonding method for silicon (Si) and indium phosphide (InP) based on a microcrystalline germanium (Ge) interlayer. The sputtered amorphous Ge (a-Ge) annealed at different temperatures exhibited different crystallinities. It is fully crystallized when the sputtering is carried out at 400 °C. For the microcrystalline Ge sputtered on the Si and InP, the Ge crystallizes along the crystal orientation of the Si, and exhibits a polycrystalline state on the InP. The crystallization evolution, bubble evolution, and bonding strength evolution at the wafer-bonded interface are investigated. The mechanism by which the bubbles are eliminated is revealed. In the case of samples featuring microcrystalline Ge grown on Si, the bonding interface consists of single crystal Ge. Bubbles can only escape from the bonding interface through atomic migration. Due to lattice mismatch and lack of gas transport channels, bubbles and dislocations form at the bonding interface. The samples with microcrystalline Ge grown simultaneously on Si substrate and InP wafer have a polycrystalline Ge layer (poly-Ge) at the bonding interface, which acts as a lattice barrier and gas transport channel. The combined action of lattice blocking and channeling effectively removes bubbles and dislocations at the bonding interface. After post-annealing, the bonding strength of the sample with fully crystallized intermediate layer can reach the bulk fracture strength of InP wafers. In addition, the carrier transport mechanism at the InP/Si bonding interface is also clearly elucidated. The above findings provide a direction for the preparation of high-performance Si-based III-V compound semiconductor photodetectors. • Microcrystalline Ge semiconductor interlayer is proposed to realize InP/Si bonding. • The InP/Si lattice is isolated by polycrystalline Ge and the dislocation nucleation is eliminated. • The crystallization status of microcrystalline Ge on Si and InP is clarified. • The process unveils bubble fade out at bonded interfaces via gas removal by atomic recombination and polycrystalline Ge. • A microcrystalline Ge layer is introduced to eliminate the influence of the oxide layer. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for friction-induced chemical reaction machining of single-crystal 4H-SiC wafers using pure iron. Material Removal Rate (MRR) and surface quality of single-crystal 4H-SiC were studied, and the results demonstrate that both high surface quality and high MRR (Ra: 2.2 nm, MRR: 375 nm/min) were obtained. The mechanism of material removal during friction was investigated by examining the critical roles of friction speed. Solid-state chemical reactions between metal and SiC surfaces can be induced by friction, and the subsequent removal of reactants, resulting in a near-damage-free machined surface. A removal mechanism model of friction was established, which reveals that both the rates of solid-state reaction and reactant removal significantly impact the final removal rate of friction. [Display omitted] • A novel friction-induced chemical removal method single crystal 4H-SiC wafer was proposed. • High surface quality and high MRR (Ra: 2.2 nm, MRR: 375 nm/min) were obtained for a 4-inch wafer. • 4H-SiC with near-damage-free surface/subsurface were obtained. • Solid-state chemical reaction occurred at low speed, pressure, and temperature. [ABSTRACT FROM AUTHOR]

Because of various purposes and high dynamic range (HDR) of brightness of objects in automotive applications, HDR image capture is a primary requirement. In this article, HDR CMOS image sensor (CIS) technology and its automotive applications are discussed including application requirements, basic HDR approaches and trends of HDR CMOS image sensor technologies, advantages and disadvantages for automotive application, and future prospect of the HDR technology. LED flicker caused by time aliasing effect and motion artifacts are two major issues in conventional multiple exposure HDR (MEHDR) approach, and several HDR technologies have been introduced for automotive applications. The advancements of image sensor fabrication technology, for instance, backside illumination (BSI) process and pixel level hybrid wafer bonding, have created new trends in the HDR technology. [ABSTRACT FROM AUTHOR]

In order to optimize the process parameters of Si-Si wafer direct bonding at room temperature, Si-Si surface activated bonding (SAB) was performed, and the effect of the argon ion beam current for surface activation treatment on the Si-Si bonding quality was investigated. For the surface activation under the argon ion beam irradiation for 300 s, a smaller ion beam current (10~30 mA) helped to realize a lower percentage of area covered by voids and higher bonding strength. Especially with the surface activation under 30 mA, the bonded Si-Si specimen obtained the highest bonding quality, and its percentage of area covered by voids and bonding strength reached <0.2% and >7.62 MPa, respectively. The transmission electron microscopy analyses indicate that there exists an ultrathin amorphous Si interlayer at the Si-Si bonding interface induced by argon ion beam irradiation to Si wafer surfaces, and its thickness increases as the argon ion beam current rises. The investigation results can be used to optimize the SAB process and promote the applications of SAB in the field of semiconductor devices. [ABSTRACT FROM AUTHOR]

Modern inelastic X-ray spectrometers employ curved, bent and diced analyzers to capture sufficiently large solid angles of radially emitted scattered radiation emanating from the sample. Fabricating these intricate analyzers, especially when a high energy resolution of a few millielectronvolts is required, is very time-consuming, expensive and often a hit-or-miss affair. A novel fabrication technique is introduced, utilizing a concave-spherical, microporous aluminium base to hold an assembly of a thin glass substrate with a diced crystal wafer bonded to it. Under uniform vacuum forces, the glass substrate is drawn into the aluminium base, achieving the desired bending radius, while dicing of the diffracting crystal layer prevents bending strain from being imposed on the individual crystal pixels. This technique eliminates the need for permanently bonding the crystal assembly to the concave lens, offering the opportunity for correcting figure errors, avoiding long-term degradation of the permanent bond, and making both lens and crystal reusable. Process and material costs are thus substantially decreased. Two analyzers, Si(844) and Ge(337) with intrinsic resolutions of 14.6 meV and 36.5 meV, respectively, were produced in this fashion and characterized in resonant inelastic X-ray scattering (RIXS) measurements. The achieved overall energy resolutions for both analyzers were 29.4 meV for Si(844) and 56.6 meV for Ge(337). Although the RIXS technique is veru sensitive to analyzer imperfections, the analyzers were found to be equal, if not superior, in quality to their traditional, permanently bonded counterparts. [ABSTRACT FROM AUTHOR]

Direct wafer bonding of β-Ga2O3 and N-polar GaN at a low temperature was achieved by acid treatment and atmospheric plasma activation. The β-Ga2O3/GaN surfaces were atomically bonded without any loss in crystalline quality at the interface. The impact of post-annealing temperature on the quality of bonding interfaces was investigated. Post-annealing at temperatures higher than 700 °C increases the area of voids at bonded interfaces probably due to the difference in the coefficient of thermal expansion. The integration of β-Ga2O3 on the GaN substrate achieved in this work is one of the promising approaches to combine the material merits of both GaN and Ga2O3 targeting the fabrication of novel GaN/β-Ga2O3 high-frequency and high-power electronics as well as optoelectronic devices. [ABSTRACT FROM AUTHOR]

The development of 5G has put forward a higher demand for filters, and the purpose of this work is fabricating surface acoustic wave (SAW) filters with excellent temperature stability and high power handling using LiTaO3/SiC bonded wafers. SAW resonators with different wavelengths are fabricated on LiTaO3/SiC, and LiTaO3/Si, bulk LiTaO3 as well. We evaluate these resonators, concluding that the bilayer substrates can enhance the performance. Subsequently, SAW filters are designed and fabricated. For the filters based on LiTaO3/SiC, the center frequency is around 2.62 GHz and the minimum insertion loss is 1.90 dB. The whole passband is flat and larger than 200 MHz, and the return loss is larger than 10 dB. SiC is more effective than Si in the enhancements of temperature stability and power handling. SiC reduces the temperature coefficient of the frequency at the left side of the passband to about half of that on LiTaO3/Si and one-sixth of that on bulk LiTaO3, and enlarges the peak power handling to 35.7 dBm. The time-to-failure of the filters on LiTaO3/SiC is 3.8 times as long as LiTaO3/Si and 11.3 times the level of bulk LiTaO3, when an input power of 30 dBm is applied ceaselessly. This work demonstrates the potential of SAW filters based on LiTaO3/SiC for RF filters in 5G. [2021-0233] [ABSTRACT FROM AUTHOR]

Semiconductor wafer bonding has gained attention for its use in the design of efficient optoelectronic devices. Here, we report the observation of the properties of semiconductor wafer bonding via metal nanoparticle arrays based on the current-voltage and reflectance measurements of multijunction solar cells. Based on our observation of temporal changes in current-voltage characteristics and reflectance, we have revealed that reduced contact resistance at the bonded interface involves two processes: van der Waals bonding, which occurs within a few minutes, and diffusion bonding of metal nanoparticles, which occurs in a time scale of days. The mechanism of wafer bonding via metal nanoparticles is discussed based on its dynamical aspects, including the roles of liquid capillarity and alloy formation at the interface. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) is a ceramic material with excellent dielectric and thermal properties, and it is used in the microelectron and energy fields. Despite polishing, the roughness (rms >10 nm) of AlN wafers fabricated by sintering fails to meet the surface requirements (rms <0.5 nm) for direct wafer bonding. However, rough-surface wafer bonding of paired AlN and AlN can be achieved with the following procedure: (1) rough surfaces are activated by oxygen plasma to introduce strong capillary action, (2) reactions of AlN and bonding species (OH−) are promoted by clamping during storage and annealing and (3) low-temperature annealing (<150 °C) joins the two surfaces of AlN/AlN by synthesizing Al 2 O 3 at the bonding interface. TEM and XPS results show that a transition layer exists between bonding surfaces wherein the concentration of nitrogen decreases while that of oxygen significantly increases. [ABSTRACT FROM AUTHOR]

Direct bonded Si-on-SiC is an interesting alternative to silicon-on-insulator (SOI) for improved thermal management in power conversion and radio frequency applications in space. We have used transient thermoreflectance and finite element simulations to characterize the thermal properties of direct bonded Si-on-4H–SiC samples, utilizing a hydrophobic and hydrophilic bonding process. In both instances, the interface has good thermal properties resulting in TBReff values of 6 + 4/−2 m2 K GW−1 (hydrophobic) and 9 + 3/−2 m2 K GW−1 (hydrophilic). Two-dimensional finite element simulations for an equivalent MOSFET showed the significant thermal benefit of using Si-on-SiC over SOI. In these simulations, a MOSFET with a 200 nm thick, 42 μm wide Si drift region was recreated on a SOI structure (2 μm buried oxide) and on the Si-on-SiC material characterized here. At 5 W mm−1 power dissipation, the Si-on-SiC was shown to result in a >60% decrease in temperature rise compared to the SOI structure. [ABSTRACT FROM AUTHOR]

Owing to the strong light–matter interactions, 2D semiconducting thin films have shown their great potential in the development of high‐performance ultraviolet–visible–near infrared (UV–Vis–NIR) broadband photodetectors (PDs). However, the planar 2D semiconducting thin films via conventional growth method are often in the form of isolated flakes and/or suffering from low absorption efficiency of light, which hinders the UV–Vis–NIR optoelectronics from widespread applications. Herein are reported high‐performance nonplanar UV–Vis–NIR broadband PD arrays, based on wafer‐scale, vertical‐structured SnSe2 nanosheet arrays (NSAs) via low‐temperature molecular beam epitaxy method. The vertical‐structured SnSe2 NSAs possess light absorption efficiency of >90% covering the wave range from 340 to 650 nm. Benefiting from the excellent light trapping ability and uniformity of waferscaled SnSe2 NSAs as well as relatively short channel, the broadband PD arrays exhibit superior comprehensive performance. They achieve a high responsivity of 31.94 A W‐1, fast speed (≈63 μs), and high uniformity. In addition, the responsivity of the broadband PD arrays is further improved via Zn‐doping technique. [ABSTRACT FROM AUTHOR]

Aluminum-to-aluminum wafer bonding is a promising technique for future wafer-level packaging and heterogeneous integration. The main challenge for a successful Al-to-Al thermocompression bonding is the fast oxidation of the aluminum surface. In this article, a surface-activated Al-to-Al wafer bonding process for patterned 200-mm wafers is presented, which removes the oxide in an argon plasma and enables a high bond quality with an accurate alignment. The influence of the bonding parameters’ temperature (200 °C–300 °C), force (20–40 kN), and activation time (2.5–5 min) on the contact resistances and bonding yield is analyzed. Additionally, we modified an etch mask during wafer fabrication and thereby improved the condition of the Al pad surface, which resulted in a higher bonding quality. Based on this optimized wafer fabrication process, we achieved a high bonding yield of >85% and contact resistances in the $\text{m}\Omega $ range for bonding temperatures as low as 250 °C. This demonstrates the potential of Al-to-Al wafer bonding to create reliable interconnects for 3-D wafer-level integration. [ABSTRACT FROM AUTHOR]

With the usage of gas ferrocene Fe(C5H5)2 as a reactant, which is different from the traditional thin Fe film, to grow the high-quality carbon nanotubes (CNTs) in the high aspect ratio (AR) trench structure, it has many advantages to be the through-silicon vias (TSVs) material for the three-dimensional (3-D) stacking technology. In this work, we successfully demonstrate the full process flow, including CNT growing, chemical–mechanical planarization (CMP), and wafer temporary bonding for CNTs as TSVs in the 3-D stacking connection. The flexibility for this demonstrated process flow makes the integration of real high dense devices and CNTs as TSVs for the 3-D connection more easily. [ABSTRACT FROM AUTHOR]

Compared to silicon substrates, III–V materials based on GaAs and/or InP are generally limited to small diameters, up to 150 mm for GaAs and 100 mm for InP, even though bulk wafers of 150 mm diameter have already been sampled. Herein, a new technology is proposed to extend the diameter of these materials by combining the Smart Cut technology, which is based on wafer bonding and layer transfer techniques, with tiling. In this unique approach, the donor substrate used in the layer transfer step is not a simple bulk wafer (limited in diameter), but a large‐diameter rebuilt wafer produced by tiling many coupons of wafers, which are cut from bulk III–V substrates of small diameter. As already established in high‐volume manufacturing schemes for silicon on insulator substrates generated through the Smart Cut process, the donor substrate can be repeatedly reclaimed and reused, allowing this approach to be economically viable. Herein, the production of an InP film of 200 mm diameter on silicon substrates is investigated and successfully demonstrated. This generic approach can be adapted to produce other large‐diameter III–V on Si substrates, including those of 300 mm diameter. [ABSTRACT FROM AUTHOR]

Capacitive micromachined ultrasonic transducer (CMUT) was introduced as an alternative to the piezoelectric thick-film-based transducers in medical imaging applications. Gradually, CMUTs have been investigated in almost all the applications in acoustics due to their superior transduction properties. CMOS compatible process flow and limitless possibilities of miniaturization made CMUT a preferred choice for the ultrasound industry. This article comprehensively reviews all the applications in which CMUT was used until now. Such a complete review of the practical applications of CMUT has not been reported elsewhere. A topicwise presentation approach is adopted, and wherever possible, the necessary details of the device properties and experimental niceties were briefly covered. [ABSTRACT FROM AUTHOR]