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In this paper, the near-carrier enhancement of phase-noise (PN) at turnover temperature ( ${T} _{to}$ ) in a quasi-thickness-Lame (QTL) mode thin-film piezoelectric-on-silicon (TPoS) oscillator is reported for the first time. QTL-TPoS resonators fabricated on degenerately-doped n-type silicon offer a ${T} _{to}$ greater than 80°C and are suitable for implementation of highly-stable ovenized oscillators. In this work, a ~123MHz QTL-TPoS resonator is heated up to ${T} _{to}$ (~90°C) by injecting current through the silicon body of the resonator. It is experimentally observed that at turnover temperature, the phase-noise slope close to the carrier frequency ( $\Delta $ f 100Hz ) decreases substantially in contrast to the expected trends. A ~10dB improvement in phase noise at 10Hz offset and a ~25dB improvement at 1Hz offset is recorded when the oscillator is operating at ${T} _{to}$ compared to room temperature. [2020-0206]

In this work, we report on the implementation of a closed-loop liquid-loaded resonant mass sensor as a test vehicle for the realization of highly sensitive miniaturized biomarker assays. Using thin-film piezoelectric-on-silicon (TPoS) contour-mode disc resonators that are specifically designed and optimized for liquid-phase operation, a liquid-loaded low power (~1.6 mW) oscillator at ~17 MHz is demonstrated with a single transistor. By proper placement of the electrodes and the supporting tethers, a high liquid-loaded quality factor (~380) and a low insertion loss (~19 dB) are concurrently achieved which enable the accurate frequency tracking of the potential mass microbalance. The frequency shifts due to the liquid-loading and the preliminary characterized frequency stability of the oscillator imply a minimum mass detection resolution in the picograms range. [2020-0177]

Lamb wave delay lines with acoustoelectri-cally-induced non-reciprocity are demonstrated in suspended lithium niobate-on-silicon waveguides for the first time. An electric current is fed through the silicon layer in the same axis as the piezoelectrically-transduced acoustic waves which are attenuated or amplified depending on the direction of the energy exchange with drifting electrons (i.e. acoustoelectric (AE) effect). Therefore, the insertion loss (IL) and non-reciprocity of the delay line is adjustable by controlling the current bias which varies the electron drift velocity and the subsequent momentum transfer. Proof-of-concept delay lines in the range of 600 MHz to 700 MHz are demonstrated with a fractional bandwidth as high as 2.8% and AE gain as high as 5.6 dB resulting in ~20 dB of non-reciprocity. These non-reciprocal components could offer a monolithic and dynamically-tunable solution to the numerous issues that arise from the increasing congestion and interferences in the telecommunication spectrum and suggests the possibility of developing fully-switchable low-IL delay lines through design/fabrication optimizations.

In this paper, Thickness-Lame (TL) mode piezoelectrically-transduced silicon resonators are studied and demonstrated. It will be shown that unlike Planar-Lame resonance modes, Thickness-Lame modes could be efficiently excited using sputtered polycrystalline piezoelectric films such as Scandium Aluminum Nitride (ScAlN) due to the constructive contribution of both $d_{31}$ and $d_{33}$ piezoelectric coefficients in the coupling coefficient. Moreover, it is shown through finite element analysis and experimental results that the coupling coefficient improves with the order of the TL harmonic mode excited in a silicon slab. It is also confirmed that the quality-factor of TL resonators substantially enhances through utilization of properly-designed acoustic reflectors (i.e. acoustic isolation frames) around the tethered resonator block. The temperature coefficient of frequency is also modeled using finite-element eigen-frequency analysis. It is shown that the turnover temperature of TL resonators aligned to the [100] plane of a degenerately-doped n-type silicon substrate varies considerably as the mode shape transitions from a Thickness-Lame to a Lateral-Extensional mode with the gradual increase of wavelength to thickness ratio. A record $Q$ of 23.2k is measured for a $\sim 185$ MHz fundamental TL resonator in vacuum ( $fxQ=4.3\times 10^{12}$ ) while quality factors of 12.6k ( $fxQ=4.6\times 10^{12}$ ) and 6k are also measured in vacuum for second- and third-harmonic TL resonators at 326 MHz and 555 MHz respectively. The combination of high turnover temperatures (>80 °C), high quality factor, and low motional resistance, promises the suitability of such resonators for extremely-stable oven-controlled oscillator applications.

Third-order nonlinear elastic coefficients of silicon have been assumed to be the dominant factor in describing the nonlinear behavior of silicon-based resonators in literature. In this article, it is postulated that in spite of the common belief, third-order elastic coefficients may not be adequate to explain the nonlinear elastic behavior of silicon micro-resonators at high n-type doping concentrations. The nonlinear behavior observed in degenerately n-type-doped bulk-extensional mode resonators aligned to $\langle {100}\rangle $ orientation is carefully studied in which a spring-hardening effect is observed at large vibration amplitudes. It is shown that the existing analytical/numerical calculations and a proposed finite element model that are based on the utilization of third-order elastic (TOE) coefficients will all predict spring-softening in such resonators, thus suggesting insufficiency of the nonlinear model.

This work presents a novel out-of-plane actuator that is composed of a single thin-film piezoelectric layer. The devices are implemented based on a platinum-coated silicon substrate to which a lithium niobate (LN) film is bonded. The out-of-plane movement of the single-layer piezoelectric film is enabled by the unique piezoelectric properties of LN, while a relatively large movement is achieved due to the large coupling coefficients of the film combined with the optimized alignment of the actuation arms to proper LN crystalline orientation. The process flow designed for the fabrication of these devices is detailed, and the preliminary test results are presented. In situ SEM imaging was conducted to quantify the amount of displacement, which is observed to be 4µm for an applied voltage of ±25V in a 250x250 µm2 device.

Long wave infrared imaging systems require small, low cost and low power systems operating at room-temperature. Seebeck nanoantennas are room temperature detectors which generate voltage due to incident electromagnetic radiation, they also provide polarization sensitivity, directivity, small footprint, tunability and the possibility of integration into electronic and photonic circuits. In this work different materials and fabrication processes used in Seebeck bowtie nanoantennas are numerically simulated in order to optimize its response in the long wave infrared region of the electromagnetic spectrum (8–14 μm.) Gold bowtie nanoantennas with thermoelectric connections made of Bi3Te2 and Sb3Te2 showed the highest responsivity values of 9 V/W for gold bowtie nanoantennas on a SiO2 substrate and 240 V/W for gold bowtie free-standing structures. Computer simulations also showed that the thermoelectric response of these detectors add linearly when connecting them in series.

In this work, we present a battery-less wireless Micro-Electro-Mechanical (MEMS)-based respiration sensor capable of measuring the respiration profile of a human subject from up to 2 m distance from the transceiver unit for a mean excitation power of 80 µW and a measured SNR of 124.8 dB at 0.5 m measurement distance. The sensor with a footprint of ~10 cm2 is designed to be inexpensive, maximize user mobility, and cater to applications where disposability is desirable to minimize the sanitation burden. The sensing system is composed of a custom UHF RFID antenna, a low-loss piezoelectric MEMS resonator with two modes within the frequency range of interest, and a base transceiver unit. The difference in temperature and moisture content of inhaled and exhaled air modulates the resonance frequency of the MEMS resonator which in turn is used to monitor respiration. To detect changes in the resonance frequency of the MEMS devices, the sensor is excited by a pulsed sinusoidal signal received through an external antenna directly coupled to the device. The signal reflected from the device through the antenna is then analyzed via Fast Fourier Transform (FFT) to extract and monitor the resonance frequency of the resonator. By tracking the resonance frequency over time, the respiration profile of a patient is tracked. A compensation method for the removal of motion-induced artifacts and drift is proposed and implemented using the difference in the resonance frequency of two resonance modes of the same resonator.

Bulk acoustic wave (BAW) thin-film lithium niobate (LN)-silicon (Si) delay lines are presented that offer more than 30 dB of non-reciprocal transmission ratio enabled by the acoustoelectric (AE) effect. In this scheme, the interaction of drifting electrons and acoustic phonons turns the microacoustic waveguide into a strong isolator. By tailoring a heterostructure stack of LN and Si, up to ~22 dB of AE gain (160 μW) is measured at only ~4 mW of DC bias power, yielding an unprecedented high power-added efficiency of 4%. This is realized within a 4.3% fractional bandwidth and a spurious-free span of 400 MHz centered around 700 MHz. Furthermore, thermal analysis and measurement results support device operation under large and continuous bias, mostly due to the high thermal conductivity of Si. The increasing demand for nonreciprocal RF components such as isolators and circulators in rapidly growing areas, namely, 5G communications and quantum computing could render this platform a potentially suitable candidate for further investigations.

A frequency-scalable reference oscillator based on a Scandium doped Aluminum Nitride-on-silicon contour-mode micromechanical resonator is demonstrated for the first time which utilizes an oscillator receiver implemented in Intel 22FFL node. The oscillator operates at 95 MHz, with a total power consumption of 1 mW including the amplitude/bias control and the shaper circuitry (@1.2 V supply). A phase noise of -107 dBc/Hz @ 1 kHz offset and an RMS jitter of 870 fs over the frequency range of 12kHz-5MHz are measured for this oscillator. Aging is also studied over a period of 25 days with a promising frequency drift of less than 4 ppm. The temperature compensated ScAlN on silicon resonator exhibited a quality factor of 5k and maximum frequency vs temperature variation of 450 ppm over the -40 °C to 125 °C temperature range making the oscillator a viable alternative for reference crystal oscillators in computing systems.

A novel resonant micro-accelerometer is implemented with an operational frequency of ~27 MHz in which an acceleration-induced change of capacitance is transformed to a frequency shift in a piezoelectric resonator utilizing the piezoelectric stiffening mechanism. In this device the mass-spring system is not embedded within the resonator, enabling a large degree of freedom in choosing the resonance frequency of the resonator. The piezoelectric resonator and the capacitive mass spring (CMS) structure are both fabricated on a silicon-on-insulator (SOI) wafer covered by a thin film of sputtered aluminum nitride. The feasibility and the efficiency of this novel sensing mechanism has been proven by demonstrating a ~600 Hz shift in the resonance frequency as the sample accelerometer was rotated 1800 yielding a 300Hz.g-1 sensitivity.

In this work a frequency-modulated (FM) resonant accelerometer operating based on the piezoelectric stiffening effect is introduced for the first time. In this device, the acceleration-sensitive variation of a capacitive mass-spring (CMS) system is up converted to a carrier frequency which is set by the resonance frequency of a thin-film piezoelectric-on-silicon (TPoS) resonator due to the piezoelectric stiffening effect. The mechanical decoupling of the acceleration-sensitive component from the resonant component allows for an additional degree of freedom in the design and a larger dynamic range, while enabling high frequency operation of the accelerometer. Proof-of-concept Z-axis accelerometers at ∼27 MHz are presented with an acceleration sensitivity of ∼300 Hz/g, The acceleration/axis sensitivity is mainly dependent on the design of the CMS and ultimately limited by the effective electromechanical coupling of the TPoS resonator.

This work demonstrates the first implementation of lithium niobate-on-silicon (LNoSi) non-reciprocal acoustic delay lines (ADL) with tunable insertion loss (IL) utilizing the acoustoelectric (AE) effect. Due to the AE effect, the direction-and the intensity-dependent momentum exchange between the drifting electrons in the Si layer and the acoustic phonons can be utilized to break the intrinsic reciprocity of the ADLs in order to control their frequency response. A 5.2 dB improvement in the IL and a 14.2 dB increase in the reverse isolation (i.e. a 19.4 dB non-reciprocal transmission ratio) is achieved through injecting a 400 µA current in one of the ADLs presented here. This opens up possibilities of merging long delays, tunable attenuators, and switches in a single miniaturized device which is a critical stepping stone in fulfillment of full-duplexed microwave systems.

Acoustoelectric delay lines (AEDL) fabricated on a composite lithium niobate-silicon (LN-Si) platform could enable acoustoelectric (AE) nonreciprocity and gain provided that the material properties of the LN-Si heterostructure are properly selected. Among such properties are the carrier density and mobility in the Si substrate. However, the bulk Si properties are subject to substantial perturbation at the LN-Si interface as a result of interfacial trapped charges at dislocations and dangling bond sites. The metal-insulator-semiconductor (MIS) capacitor inherently formed in such heterostructures, however, could allow for some level of control over the Si carrier distribution at the LN film interface. In this work, we demonstrate that the AE gain achieved by the momentum transfer from the carriers drifting in Si and the subsequent nonreciprocity could be fine-tuned and the efficiency of the device could be improved by utilizing the MIS capacitor. The device efficiency is found to be enhanced once the majority electron carriers in n-type Si are slightly depleted at the LN-Si interface resulting in ∼1.5 times improvement in the AE gain at a lower bias current, increasing the efficiency by ∼60%.

This paper reports the first study of near-carrier phase noise (PN) dependency on the resonator volume/harmonic-number in thin-film piezoelectric-on-substrate (TPoS) MEMS oscillators. Two lateral bulk-acoustic TPoS resonators with different volumes (3rd and 5th harmonic orders) were designed to operate at the same ∼25.6 MHz and fabricated on a $25\mu\mathrm{m}$ silicon on insulator (SOI) substrate. The devices chosen for this study have different volumes but exhibit identical Quality factor ( $Q$ ) and insertion loss (IL). The measured PN of the oscillators built based on these two resonators are measured and it is observed that the one based on the 5th order resonator exhibits ∼6dB lower PN @1KHz frequency offset compared to the 3rd order device. Although our preliminary results are not conclusive enough, it is hypothesized that an inverse proportionality to the resonator volume/mass predicted by earlier models could also describe this observation.

Here we present the first instance of passive wireless MEMS flow rate sensor designed to measure respiratory flow rate and profile using the time-of-flight sensing modality without the need for battery or on-sensor circuits. With a footprint of only 7.2cm2, the sensor can measure human respiratory rate and flow when placed close to the nasal airway using an excitation antenna that transmits an average power of ∼5mW at a ∼75cm distance. To facilitate the time-of-flight sensor, two low loss, high quality factor TPoS MEMS resonators are placed ∼1cm apart and are connected to a small (3.8cm2) planar ground antenna. We were able to measure flow rate and respiration profile of human subject from a distance of 20cm from the base transceiver. In addition to flow rate, we were capable of accurately tracking the respiration profile of the patient and successfully detecting short cessation of breathing events commonly used in diagnosing sleep apnea.

In this article, the microfluidic channels that deliver liquid to a microscale thin-film piezoelectric-on-silicon (TPoS) gravimetric resonant sensor are incorporated into the backside of the silicon-on-insulator (SOI) wafer on which the resonator is fabricated. Specifically, a microwell is embedded at the bottom of the disk -shaped TPoS resonator, while a very thin layer of parylene covering the backside of the resonator and the microwell forms an isolation layer between the liquid and the top device-layer features. In this way, the liquid is in contact with the backside of the resonator, while the device-defining trenches and the electrical connections to the resonator stay clear, thus mitigating the acoustic energy loss and undesirable feedthroughs. The impact of the parylene layer thickness on a few symmetric ( ${S}$ ) and antisymmetric ( ${A}$ ) Lamb wave modes of the resonator is experimentally studied, and the performance of such modes in the liquid is characterized by filling the microwells through a PDMS-based microfluidic channel. The parylene layer, while marginally affecting the resonator in the air, is found to substantially enhance its performance in the liquid media. Strong resonance peaks with high quality factors ( ${Q}$ ) are observed for the ${S}$ modes, among which ${Q}$ values above 400 are recorded for a specific mode named ${S}$ ( 4 , 2 ) (among the highest ever reported). This article can potentially facilitate the realization of highly stable and sensitive resonant mass sensors (i.e., microbalance) for real-time applications. Additionally, the effect of the acoustic energy radiation in the form of evanescent shear and longitudinal waves in liquid on the ${Q}$ and resonance frequency of the disk resonators is experimentally validated.

In this work a novel surface treatment is applied to thin-film piezoelectric-on-silicon disc resonators that enables liquid phase operation of the resonator while maintaining a high quality factor (Q). By coating the backside and the surrounding trenches of the resonator with Parylene-C, a biocompatible insulation layer is formed that completely avoids the penetration of liquid into small gaps while enabling the surface functionalization for various sensing purposes. The effect of viscous damping on different vibration modes of the disc resonator is investigated and a high order contour mode is identified at 17.2 MHz which exhibits the least drop in the quality factor (Q) when operated in liquid media. A record Q of 440 is measured for this resonance mode in water, corresponding to a ~55% reduction from the Q measured in air. Such high Q values in water facilitate implementation of high resolution liquid-phase mass sensors for biomedical or industrial applications.

We review some emerging trends in transduction, connectivity and data analytics for Point-of-Care Testing (POCT) of infectious and non-communicable diseases. The patient need for POCT is described along with developments in portable diagnostics, specifically in respect of Lab-on-chip and microfluidic systems. We describe some novel electrochemical and photonic systems and the use of mobile phones in terms of hardware components and device connectivity for POCT. Developments in data analytics that are applicable for POCT are described with an overview of data structures and recent AI/Machine learning trends. The most important methodologies of machine learning, including deep learning methods, are summarised. The potential value of trends within POCT systems for clinical diagnostics within Lower Middle Income Countries (LMICs) and the Least Developed Countries (LDCs) are highlighted.

In this work, evidence for acoustoelectric (AE) amplification in lateral-extensional thin-film piezoelectric-on-silicon (TPoS) resonant cavities for the first time is demonstrated. Due to the piezoelectric coupling, an evanescent electromagnetic wave is induced in the silicon (Si) layer that is a part of the resonant cavity, exchanging momentum with the carriers. Therefore, by injecting an electric current in this layer, the acoustic equivalent of Cherenkov radiation – AE amplification – can be realized. Such phenomenon is observed in a 1 GHz TPoS resonant cavity in which lateral field excitation is utilized to excite the acoustic wave.

In this paper it is shown that bulk-extensional resonance modes could be efficiently excited in silicon blocks aligned to non-major crystalline planes without compromising the performance (i.e. quality factor and coupling). This is accomplished through optimization of the silicon block dimensions and the metal electrode pattern to enable efficient excitation of the asymmetric lateral-extensional mode in a resonator aligned to 22.5 degrees off $ $ or $ $ silicon crystalline planes. The motivation for off-axis designs is to use the rotation angle as a design parameter to achieve enhanced mechanical linearity in degenerately-doped n-type silicon resonators. The amplitude-frequency coefficient ($K$) is calculated for three block resonators that are fabricated on a 40 $\mu {\mathrm{ m}}$ thick n-type (N$\cong$ 4.6e19 to 7.3e19 cm$^{-3}$) SOI substrate and aligned to different crystalline planes. Experimental results show that the amplitude-frequency coefficient of devices rotated 22.5 degrees off $ $ plane is significantly lower than those aligned to $ $ and $ $ planes by a factor of 0.05 and 0.28, respectively.

Thickness harmonics in Cross-Sectional Quasi Lame Mode (CQLM) thin-film piezoelectric-on-silicon (TPoS) resonators are demonstrated for the first time. Harmonic CQLM TPoS resonators are expected to exhibit higher coupling factor compared to the fundamental thickness modes as confirmed in this paper. The CQLM-TPoS resonators of this work are fabricated on a $40\mu$m thick silicon on insulator (SOI) substrate with three different finger pitches (40$\mu {\mathbf {m}, 20} \mu \textbf{m}$ and 15$\mu$m) to actuate first, second and third harmonics in the thickness of the resonator. Measured quality factors as high as 10,500, 8,700 and 3,300 are reported for the first, second and third harmonic CQLM-TPoS resonators at 76 MHz, 150 MHz, and 220 MHz respectively. Measured coupling factor is almost 5 times higher for the third thickness harmonic mode compared to the first thickness harmonic.

Thin-film piezoelectric-on-silicon (TPoS) disc resonators, operating in 4–1 contour mode around 17.2 MHz, are coated with Parylene from the backside to form a biocompatible insulation layer that enables operation of the resonator in liquid media. The backsides of the resonators are chosen to be large to form a microwell that generates boundaries to the liquid assays and the diameter of such microwells is varied to allow for studying the effect of its size on the performance of the resonator under viscous damping. The results displayed very high quality factors ($Q$) in water, from 315–440, that are consistently affected by the size of microwells.

In this paper, anisotropy of single-crystalline silicon (SCS) is exploited to enable side-supported radial-mode thin-film piezoelectric-on-substrate (TPoS) disk resonators. In contrast to the case for isotropic material, it is demonstrated that the displacement of the disk periphery is not uniform for the radial-mode resonance in SCS disks. Specifically, for high-order harmonics, nodal points are formed on the edges, creating an opportunity for placing suspension tethers and enabling side-supported silicon disk resonators at the very high-frequency band with negligible anchor loss. In order to thoroughly study the effect of material properties and the tether location, anchor loss is simulated using a 3-D perfectly matched layer in COMSOL. Through modeling, it is shown that eighth-harmonic side-supported SCS disk resonators could potentially have orders of magnitude lower anchor loss in comparison to their nanocrystalline diamond (NCD) disk resonator counterparts given the tethers are aligned to the [100] crystalline plane of silicon. It is then experimentally demonstrated that in TPoS disk, resonators fabricated on an 8- $\mu \text{m}$ silicon-on-insulator (SOI) wafer, unloaded quality factor improves from ~450 for the second-harmonic mode at 43 MHz to ~11500 for the eighth-harmonic mode at 196 MHz if tethers are aligned to [100] plane. The same trend is not observed for NCD disk resonators and SCS disk resonators with tethers aligned to [110] plane. Finally, the temperature coefficient of frequency is simulated and measured for the radial-mode disk resonators fabricated on the 8- $\mu \text{m}$ -thick degenerately n-type doped SCS, and the TFC data are utilized to guarantee proper identification of the harmonic radial-mode resonance peaks among others.

We describe two designs for a variable attenuator of infrared laser radiation. The principle is based on the excitation of surface plasmon polaritons with prism couplers on suitable conductors. Practical considerations dictate the use of conductors with infrared plasma frequency. An intensity variation of more than nine-orders is theoretically demonstrated. Both designs involve mechanical displacements of optical elements by less than several microns, which in principle might be much faster than current art for variable attenuators of IR laser beams. One design provides fine control at high attenuation. Experimental demonstrations support the predicted function.

Recent commercialization has peaked interest in transparent conducting oxides being implemented in transparent applications. Gallium doped zinc oxide (GZO) films exhibit excellent transmission characteristics in the visible spectrum while maintaining high electrical conductivity. In majority applications the work function of the material used has an impact on the device performance as it affects the energy barrier height at the hetero-junction interface. Hence, the work function identification is of critical importance. In this article, we discuss work function extraction of GZO from a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) device for the first time. Four level mask sets were used to fabricate two MOSFET devices following exact same conditions. Source and drain contacts were made using aluminum metal for both MOSFETs. One of the MOSFET was fabricated with aluminum as gate contact and the other MOSFET with transparent conducting GZO as its gate contact. GZO used in this research were RF sputtered. From the threshold voltage equation of both the fabricated MOSFETs, work function of GZO was extracted. The electrical and optical transmission studies were also performed on the sputtered GZO thin films and are reported in this study.

Recent commercialization has peaked interest in transparent conducting oxides being implemented in transparent applications. Gallium doped zinc oxide (GZO) films exhibit excellent transmission characteristics in the visible spectrum while maintaining high electrical conductivity. In majority applications the work function of the material used has an impact on the device performance as it affects the energy barrier height at the hetero-junction interface. Hence, the work function identification is of critical importance. In this article, we discuss work function extraction of GZO from a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) device for the first time. Four level mask sets were used to fabricate two MOSFET devices following exact same conditions. Source and drain contacts were made using aluminum metal for both MOSFETs. One of the MOSFET was fabricated with aluminum as gate contact and the other MOSFET with transparent conducting GZO as its gate contact. GZO used in this research were RF sputtered. From the threshold voltage equation of both the fabricated MOSFETs, work function of GZO was extracted. The electrical and optical transmission studies were also performed on the sputtered GZO thin films and are reported in this study.

In this work, a technique is introduced for isolating the energy loss associated with the interaction of charge carriers with acoustic phonons in thin film piezoelectric-on-silicon (TPoS) MEMS resonators. This method facilitates the investigation of acoustoelectric loss mechanism. The variation in quality factor (Q) and insertion loss of high frequency TPoS resonators is reported while the surface carrier concentration of the silicon layer is varied through application of a voltage to the metal-dielectric-silicon capacitor that is intrinsically formed during the conventional fabrication of TPoS resonators. A maximum of 3% improvement in the insertion loss (IL~9 dB) of a ~926 MHz resonance mode is recorded when a 4 V bias is applied to the said capacitance which is believed to stem from a reduction in interaction of acoustic phonons with carriers.