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Diamond has many appealing properties, including biocompatibility, ease of surface modification, and chemical-physical stability. In this study, the temperature dependence of the pH-sensitivity of a oxygen-terminated boron-doped diamond solution gate FET (C-O BDD SGFET) is reported. The C-O BDD SGFET operated in an electrolyte solution at 95 °C. At 80 °C, the pH sensitivity of C-O BDD SGFET dropped to 4.27 mV/pH. As a result, we succeeded in developing a highly sensitive pH sensing system at -54.6 mV/pH at 80 °C by combining it with a highly pH sensitive stainless-steel vessel.

This paper describes a deoxyribonucleic-acid-sensitive electrolyte solution-gate field-effect transistor (SGFET) sensor utilizing a partial carboxyl-terminated boron-doped polycrystalline diamond surface as a linker to connect a deoxyribonucleic acid (DNA) probe. A high density of carboxyl termination on the polycrystalline diamond surface that was employed as a FET channel was achieved using a vacuum ultraviolet system with oxygen gas. A single-stranded DNA probe was immobilized on the polycrystalline diamond channel via amino coupling. The current-voltage characteristics of the polycrystalline diamond SGFET sensor was examined with bias voltages within its potential voltage window. The characteristics of the drain-source current verses the drain-source voltage showed a pinch-off, a shift voltage of up to 40 mV with a coefficient of variation of 4 - 11% was obtained between hybridization and denaturation. In addition, a single nucleotide mutation of DNA sequence was selectively recognized by the shift voltage up to ca. 10 mV.

Diamond is a promising material for merging solid-state and biological systems owing to its chemical stability, low background current, wide potential window and biocompatibility. The effects of surface charge density on human immunodeficiency virus type 1 Trans-activator transcription (HIV-1 Tat) protein binding have been investigated on a diamond field-effect transistor (FET) using ribonucleic acid (RNA) aptamers as a sensing element on a solid surface. A change in the gate potential of 91.6 mV was observed, whereby a shift in the negative direction was observed at a source-drain current of -8 μA in the presence of HIV-1 Tat protein bound to the RNA aptamers. Moreover, the reversible change in gate potential caused by the binding and regeneration cycles was very stable throughout cyclical detections. The stable immobilization is achieved via RNA aptamers covalently bonded to the carboxyl-terminated terephtalic acids on amine sites, thereby increasing the sensitivity of the HIV-1 Tat protein sensor. The reliable use of a real sample of HIV-1 Tat protein by an aptamer-FET was demonstrated for the first time, which showed the potential of diamond biointerfaces in clinical biosensor applications., (Copyright © 2012 Elsevier B.V. All rights reserved.)

An aptasensor was designed on a nanocrystalline diamond (NCD) surface that combined with biological recognition elements, PDGF-binding aptamers, which inherently possess high affinity to PDGF-BB proteins. Functional components such as carboxylic acids (-COOH) and amines (-NH2) were directly introduced onto the NCD surface and used as probing units for immobilization of PDGF-binding aptamers. The surface coverage of different components on the NCD was analyzed by X-ray photoelectron spectroscopy (XPS) measurements, and the effects of various functionalizations on the NCD biosensor performance were investigated via fluorescence observations. The coverages of carboxyl and amine groups achieved were 12 and 23%, respectively, for the directly aminated and carboxylated NCD; however, the lower density of carboxyl groups on the functionalized surface did not deteriorate the performance of the COOH-NCD biosensor. Fluorescence investigations demonstrated comparable performance in sensitivity and selectivity for PDGF protein detection on COOH-NCD and NH2-NCD biosensors. Multiple regeneration tests clearly showed that the COOH-NCD biosensor as well as the NH2-NCD biosensor retained a high performance without exhibiting any noticeable degradation.

Aptamer-based fluorescence detection of platelet-derived growth factor (PDGF) on a functionalized diamond surface was demonstrated. In this work, a sandwich design based on the ability of PDGF to bind with aptamers at its two available binding sites was employed. It was found that this sandwich design approach significantly increases the fluorescence signal intensity, and thereby a very low detection limit of 4 pM was achieved. The effect of the ionic strength of MgCl(2) buffer solution was also investigated, and the most favourable binding for PDGF-BB occurred at a Mg(2+) concentration of 5.5 mM. Since the aptamers bind to the target PDGF with high affinity, fluorescence detection exhibited high selectivity towards different biomolecules. The high reproducibility of detection was confirmed by performing three cycles of measurements over a period of three days.

A solution gate field effect transistor (SGFET) using an oxidised boron δ-doped channel on (111) diamond is presented for the first time. Employing an optimised plasma chemical vapour deposition (PECVD) recipe to deposit δ-layers, SGFETs show improved current-voltage (I-V) characteristics in comparison to previous similar devices fabricated on (100) and polycrystalline diamond, where the device is shown to operate in the enhancement mode of operation, achieving channel pinch-off and drain-source current saturation within the electrochemical window of diamond. A maximum gain and transconductance of 3 and 200μS/mm are extracted, showing comparable figures of merit to hydrogen-based SGFET. The oxidised device shows a site-binding model pH sensitivity of 36 mV/pH, displaying fast temporal responses. Considering the biocompatibility of diamond towards cells, the device's highly mutable transistor characteristics, pH sensitivity and stability against anodic oxidation common to hydrogen terminated diamond SGFET, oxidised boron δ-doped diamond SGFETs show promise for the recording of action potentials from electrogenic cells., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Here, we report a novel method of micropatterning oligonucleotides via aromatic groups as linkers on partially amino-terminated diamond and the inherence on subsequent hybridization. The covalent immobilization of probe oligonucleotides and characterization of immobilized probe oligonucleotides with carboxylic compounds were investigated by X-ray photoelectron spectroscopy (XPS). To confirm the effects of linker flexibility in a low amino group on diamond for probe oligonucleotides, three kinds of dicarboxylic compound--adipic acid, terephthalic acid, and trimesic acid--were used for immobilization of probe oligonucleotides, like linkers; and these oligonucleotides were hybridized with target oligonucleotides labeled with Cy 5 on the micropatterned diamond surface. The hybridization intensities determined by epifluorescence microscopy were compared and analyzed.

We have investigated the electrolyte-solution-gate field effect transisitors (SGFETs) used hydrogen terminated (H-terminated) or partially oxygen terminated (O-terminated) polycrystalline diamond surface in the Cl- and Br- ionic solutions. The H-terminated channel SGFETs are insensitive to pH values in electrolyte solutions. The threshold voltages of the diamond SGFETs shift according to the density of Cl- and Br- ions about 30 mV/decade. One of the attractive biomedical applications for the Cl- sensitive SGFETs is the detection of chloride density in blood or in sweat especially in the case of cystic fibrosis. The sensitivities of Cl- and Br- ions have been lost on the partially O-terminated diamond surface. These phenomena can be explained by the polarity of surface change on the H-terminated and the O-terminated surface.

Diamond is a wide bandgap semiconductor (bandgap: 5.5 eV). However, through impurity doping, diamond can become a p-type or n-type semiconductor. The minimum resistivity of p-type semiconductor diamond is less than 10−3 Ω cm, which is no more than that of silicon (Si). In contrast, the minimum resistivity of n-type diamond is as high as 103 Ω cm. At present, the development of unipolar devices such as p-channel field-effect transistors (p-FETs) based on diamond is strongly anticipated. When the diamond surface is terminated using hydrogen (H) or Si atoms, the subsurface layer becomes a p-type accumulation layer or inversion layer that forms a two-dimensional hole gas (2DHG), which can then be used as a channel for a FET structure. As a p-FET, the performance of this device approaches that of other wide bandgap semiconductor n-channel FETs. One of the main advantages of this diamond p-FET is that the p-type accumulation or inversion layer is formed natively on the hydrogen terminated (C–H) diamond. This review describes the low metal contact resistance that induces 2DHG formation on the C–H diamond surface, on which negatively charged sites are formed. The negatively charged surface model explains the 2DHG formation clearly based on the FET's operating mechanism. Recent advances in 2DHG FETs are also discussed, particularly in terms of their current densities of >1 A mm−1 and their high frequency performance. Finally, we propose two types of complementary high-voltage circuit that combine diamond p-FETs with other wide bandgap semiconductor n-FETs. [ABSTRACT FROM AUTHOR]

A novel method to fabricate the oxidized silicon-terminated (C–Si–O) diamond metal-oxide-semi- conductor field-effect transistors (MOSFETs) by replacing the retained SiO2 masks with an atomic layer deposition (ALD)-Al2O3 film as the main gate insulator was proposed for the first time. Compositional analysis across the SiO2 masks and on the air-exposed C–Si–O (111) diamond surface has been carried out by utilizing secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) techniques, respectively. Furthermore, we revealed that, under selectively epitaxial growth of diamond through a SiO2 mask, a carbon-rich film was formed on SiO2 and C–Si bonding was realized at the SiO2/(111) diamond interface. The fabricated device with a source and drain distance (${L}_{SD}$) of $3 \,\mu \text{m}$ exhibits a distinct threshold voltage (${V}_{TH}$) of −5.6 V and a maximum drain current density (${I}_{D\_{}{MAX}}$) up to −311 mA/mm, which is a record value among normally-off single-crystalline diamond MOSFETs to date. In the case of having ALD-Al2O3 as the main gate insulator, normally-off operation of the C–Si–O diamond MOSFETs has a stark contrast with the typically normally-on performance of the hydrogen-terminated (C–H) diamond MOSFETs, which is mainly due to the smaller negative electron affinity of C–Si–O diamond compared with that of C–H diamond. These results indicate that the proposed C–Si–O (111) diamond MOSFETs with excellent normally-off operation and large drain current density are promising to fulfill the requirements of fail-safe and current drive capabilities in power device applications. [ABSTRACT FROM AUTHOR]

This letter reports on the high voltage operations and high temperature operations of the transparent polycrystalline diamond field-effect transistor (TPD-FET). The devices were fabricated with a wide range of wide gate-drain lengths (${L}_{\textit {GD}}$) and a thick Al2O3 passivation layer of 400 nm. Voltage breakdowns of more than 1000 V have been observed in high voltage measurements. The temperature dependence and performance of the devices at RT to 673 K were also shown. As the temperature was varied, the maximum drain currents (${I}_{{D max}}$) for different ${L}_{\textit {GD}}$ devices increased significantly from 33.8 mA/mm – 72.8 mA $/$ mm to 86.0 mA/mm - 116.4 mA $/$ mm in terms of absolute values. The findings demonstrate the advantages and potential of diamond-based devices in high temperature conditions. [ABSTRACT FROM AUTHOR]

This letter reports a high drain current density and normally-off operation metal-oxide-semiconductor field-effect transistors (MOSFETs) with a gate insulator of 100 nm-Al2O3. A heavily boron-doped layer as the source/drain region was deposited on a (110) polycrystalline diamond substrate to achieve a low ohmic contact resistance. The MOSFETs demonstrate a maximum current density of −400 mA mm $^{-{1}}$ normalized by gate width and a maximum current density of $- 2000\,\,\mu \text{m}$ mA mm−1 normalized by gate length and gate width, which are the highest values for normally-off diamond FETs. The Grain boundaries (GBs) and the nitrogen impurities ($\sim {3}\,\,\times \,\,{10}^{{17}}$ cm $^{-{3}}$) as ionized donors in the channel region caused the threshold voltage (${V}_{\text {th}}$) to shift in the negative direction, exhibiting normally-off characteristics. This technique provides a promising method to achieve high-performance diamond devices, and help improve safety and save energy in switching systems. [ABSTRACT FROM AUTHOR]

In this article, the normally- OFF oxidized Si-terminated (C–Si) diamond metal–oxide–semiconductor field-effect transistors (MOSFETs) with as-deposited 0.5-nm silicon on diamond annealed at high temperature as the subsurface p-channel were presented for the first time. A novel method utilizing both a metal mask to realize the regrown heavily boron-doped (001) diamond layer first (p+-diamond-first) and a molecular beam deposition (MBD) method to procure atomic-scale silicon deposition was achieved. Scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) element mapping results suggest that the C–Si diamond/Al2O3 interface is quite continuous and atomically flat. A remarkably high threshold voltage (${V}_{\text{TH}}$) of −10 V and a maximum drain current density (${I}_{D\_{}{\text{MAX}}}$) of −156 mA/mm are simultaneously achieved in the fabricated devices. The devices with different source and drain (S/D) distances ($L_{\text{SD}}$) deliver robust ${V}_{\text{TH}}$ results and feature low OFF-state S/D leakage current $\vert {I}_{\text{leakage}}\vert $ of ~ $6\times10$ −6 mA/mm at ${V}_{\text{GS}}$ = 0 V. The extracted field-effect mobility is as high as 127 cm2 $\cdot \text{V}$ −1 $\cdot \text{s}$ −1 and the interface state density is as low as $4.35\times10$ 12 eV−1 $\cdot $ cm−2. These competitive results reveal that this first attempt of employing the combination of p+-diamond-first and MBD approaches promotes the integration of the advanced silicon manufacturing process with wide bandgap diamond material for power applications. [ABSTRACT FROM AUTHOR]

Hole concentration of 2-D hole gas (2DHG) on (110) diamond is higher than that on other faces, making it the best choice for power device application. Detailed analysis of atomic layer deposition (ALD) Al2O3/(110) C–H diamond interface structure is of vital importance. MOSFETs with thin (10 nm) and thick (100 nm) ALD Al2O3 layer were made in this study. The microstructure of Al2O3 on (110) C–H diamond was analyzed. Abrupt interface of ALD Al2O3/C–H diamond was observed through high resolution transmission electron microscope (HRTEM). Cascode structure using diamond MOSFETs and enhancement mode silicon MOSFET is fabricated and its high performance is confirmed. [ABSTRACT FROM AUTHOR]

This letter reports the successful demonstration of large-current and high-voltage (001) vertical-type two-dimensional hole gas (2DHG) diamond trench metal-oxide-semiconductor field-effect transistors (MOSFETs) with a p−-drift layer. The fabricated transistor demonstrated a maximum drain current density of 210 mA/mm, a field-effect-mobility of 61 cm2V−1s−1, and a specific on-resistance of 23 $\text{m}\Omega $ cm2. Moreover, a high breakdown voltage of 580 V with a gate-drain length of 10 $\mu \text{m}$ was obtained, which is the highest value reported for a vertical-type diamond MOSFET to date. These characteristics indicate that a vertical-type diamond MOSFET using a p−-drift layer may be used to realize a p-channel power device with a high breakdown voltage and low on-resistance. [ABSTRACT FROM AUTHOR]

This article reports on the high operation voltage large-signal performance of two-dimensional hole gas diamond metal–oxide semiconductor field-effect transistors (MOSFETs) with thick atomic-layer-deposition (ALD)-Al2O3 formed on high purity polycrystalline diamond with a (110) preferential orientation. MOSFETs with a 1- $\mu \text{m}$ gate-length having a gate oxide layer of 200-nm-thick Al2O3, formed by ALD and asymmetric structures, to withstand high-voltage operations. The large-signal performances were evaluated at a quiescent drain voltage of greater than −60 V for the first time in diamond field-effect transistor (FET). As a result, an output power density of 2.5 W/mm under class-A operation at 1 GHz, which is higher than that of diamond FETs fabricated by a self-aligned gate process, was obtained. Moreover, an output power density of 1.5 W/mm was exhibited by the MOSFET when biased at a quiescent drain voltage of −40 V under class-AB operation at 3.6 GHz using an active load-pull system. This is the highest recorded value for diamond FETs at a frequency greater than 2 GHz, owing to the high-voltage operation. These results indicate that diamond p-FETs under high-voltage operations are the most suitable for high-power amplifiers with complementary circuits. [ABSTRACT FROM AUTHOR]

Diamonds are highly favored materials in high-temperature and high-power operations owing to their excellent characteristics, and diamond p-channel field-effect transistors (p-FETs) considerably aid in the improvement of CMOS technology, providing high performance, which is essential for inverter operations. This study demonstrates a low ON-resistance (001) vertical-type two-dimensional hole gas (2-DHG) diamond metal–oxide–semiconductor field-effect transistor (MOSFET) with a trench gate structure. The active area of the device reduced after introducing a trench gate structure that can significantly improve the device integration and high-current operation. The maximum drain current density (ID) exceeds 20 kA/cm2 at VDS = −50 V and VGS = −20 V, which is the highest value obtained for (001) vertical-type diamond MOSFETs. This vertical-type diamond trench MOSFET can obtain the lowest ON-resistance (RONS) of 2.5 mΩ⋅ cm2, which is comparable to that of SiC and GaN vertical-type n-channel FETs (n-FETs). It can be potentially used as a p-channel power FET in a complementary inverter. Furthermore, this study demonstrates that the trench contact depth to the p+ diamond substrate significantly impacts the static characteristics of a device using the ATLAS device simulation. This result significantly contributes to the improvement of the rising drain current in the low-voltage region of the vertical-type diamond FET, which can be used in the future as p-channel power devices for the next generation of complementary inverters using GaN or SiC MOSFETs as n-channels. [ABSTRACT FROM AUTHOR]

We report two-dimensional hole gas (2DHG) diamond field-effect transistors (FETs) with microwave plasma chemical vapor deposition (MPCVD)-regrown p+-diamond (B concentration $\sim \,\,1\times 10 ^{22}$ /cm3) ohmic contacts. The heavily doped p+-diamond shows low ohmic contact resistance of $1.1~\Omega \cdot $ mm, which is the lowest value reported in diamond to date. In addition, the p+-diamond with a TiC also offers much stronger metal adhesion when compared with previous Au/hydrogen-terminated diamond surfaces and is suitable for industrial use. Benefiting from the low contact resistance of the p+-diamond layer, a maximum drain current density of 1170 mA/mm and an ON-resistance of $8.9~\Omega \cdot $ mm were demonstrated in a 2DHG diamond metal-oxide-semiconductor FET with a $1~\mu \text{m}$ gate length. These results indicate that the regrown p+-diamond ohmic contacts will make it possible to realize further improvements in the maximum drain current density of 2DHG diamond FETs. [ABSTRACT FROM AUTHOR]

The feasibility of titanium oxide (TiOx) encapsulation of the source/drain metal contacts of diamond solution‐gate field‐effect transistor (SGFET) for biosensor applications is explored. The SGFETs fabricated by this method show excellent FET characteristics. For comparison, the electrical characteristics performance of SGFET TiOx encapsulated devices with two different channel lengths of 100 and 1.5 μm is investigated. The miniature device with a channel length of 1.5 μm exhibits remarkable enhancement of the maximum output current and transconductance (gm) to 3000 μA mm−1 and 11.3 mS mm−1, respectively. Furthermore, the scaling gm behavior of diamond SGFETs is experimentally studied by means of the channel length for the first time. The gm is enhanced when the channel length is reduced. The double‐layer capacitance of the diamond SGFET devices with channel mobility of 6–11 cm2 (V s)−1 is estimated to be 3–5 μF cm−2 across the channel length which is adequate for biosensor applications. [ABSTRACT FROM AUTHOR]

Hydrogen-terminated (C-H) diamond has a high current density owing to the 2-D hole gas (2DHG) on its C-H diamond surface. The C-H diamond metal-oxide-semiconductor field-effect transistor (MOSFET) has high-breakdown-voltage characteristics but exhibits normally-ON operation. For security and energy-saving purposes, we fabricated the diamond cascode using the C-H diamond p-channel field-effect transistor (p-FET) combination with the normally- OFF silicon p-FET. The diamond cascode exhibits normally- OFF characteristics and a high breakdown voltage of more than 1.7-kV. [ABSTRACT FROM AUTHOR]

We present a miniaturized vertical-type two- dimensional hole gas (2DHG) diamond metal-oxide-semiconductor field-effect transistor (MOSFET) by adopting a gate-source overlapping structure. We developed a 2- $\mu \text{m}$ -wide trench and disposed a part of the gate electrode to overlap the Al2O3 insulator film on the source electrode to eliminate the space between source and gate electrode. We obtained the maximum drain current density of ${I}_{\text {D}} =12800$ A/cm2 at ${V}_{\text {DS}} = -50$ V and the specific on-resistance of ${R}_{\text {ON}}=3.2\,\,\text{m}\Omega $ cm2 at ${V}_{\text {DS}} = -10$ V and confirmed their improvement by the miniaturization of devices and reduction of source to gate resistance. In addition, the drain current on/off ratio was 7 orders magnitude even at 200 °C with the formation of a highly concentrated, thick nitrogen-doped layer as the current blocking layer. [ABSTRACT FROM AUTHOR]

Diamond is a promising material for power applications owing to its excellent physical properties. Two-dimensional hole gas (2DHG) diamond metal–oxide–semiconductor field-effect transistors (MOSFETs) with hydrogen-terminated (C-H) channel have high current densities and high breakdown fields but often show normally- ON operation. From the viewpoint of safety, normally- OFF operation is required for power applications. In this letter, we used ion implantation to form a shallow and thin nitrogen-doped layer below the C-H channel region, which realized normally- OFF operation. Nitrogen-ion implanted length is fixed at 5 or 10 $\mu \text{m}$. Nitrogen is a deep donor (1.7 eV) and the nitrogen-doped layer prevents hole accumulation near the surface. The threshold voltage was as high as −2.5 V and no obvious dependence on the threshold voltage of nitrogen-ion implanted length is observed. The breakdown field was 2.7 MV/cm at room temperature. Of 64 devices with a common gate length, 75% showed normally- OFF operation. We confirmed the threshold voltage shift by a thin and shallow nitrogen-doped layer formed by ion implantation. [ABSTRACT FROM AUTHOR]

This letter reports the small-signal and large-signal performances at high drain voltage ($\text{V}_{\textsf {DS}}$) ranging up to 60 V for a 0.5 $\mu \text{m}$ gate length two-dimensional hole gas diamond metal-oxide-semiconductor field-effect transistor with a 100-nm-thick atomic-layer-deposited Al2O3 film on a IIa-type polycrystalline diamond substrate with (110) preferential surfaces. This diamond FET demonstrated a cutoff frequency ($\text{f}_{\textsf {T}}$) of 31 GHz, indicating that its carrier velocity was reaching $\textsf {1.0}\times \textsf {10}^{\textsf {7}}$ cm/s for the first time in diamond. In addition, a $\text{f}_{\textsf {T}}$ of 24 GHz was obtained at $\text{V}_{\textsf {DS}}=-\textsf {60}$ V, thus giving a $\text{f}_{\textsf {T}}\times \textsf {V}_{\textsf {DS}}$ product of 1.44 THz $\cdot \text{V}$. This diamond FET is promising for use as a high-frequency transistor under high voltage conditions. Under application of a high voltage, a maximum output power density of 3.8 W/mm (the highest in diamond) with an associated gain and power added efficiency were 11.6 dB and 23.1% was obtained when biased at $\text{V}_{\textsf {DS}}=-\textsf {50}$ V using a load-pull system at 1 GHz. [ABSTRACT FROM AUTHOR]

The exceptional performance of diamond-based field-effect transistor technology is not restricted to devices that use single crystalline diamond alone. This letter explores the full potential of the heteroepitaxial diamond field-effect transistor (HED-FET). HED-FET devices were fabricated with a long gate–drain length ( L\textsf {GD} ) configuration using C–H bonded channels, and a high maximum current density of 80 mA/mm and a high I_ \mathrm\scriptstyle ON/I_ \mathrm\scriptstyle OFF ratio of 109 were achieved. Additionally, the HED-FETs showed an average breakdown voltage of ≥500 V and comparatively high breakdown voltage of more than 1 kV. This letter represents a significant step toward the realization of the potential of widely available heteroepitaxial diamond for use in FET applications. [ABSTRACT FROM AUTHOR]

A vertical edge graphite layer (VEG) fabricated on a diamond (001) substrate and the recovery of the crystallinity of the diamond substrate following high-dose ion implantation and high-temperature annealing (HTA) was investigated. The Al ions were implanted into the diamond (001) surface at 773 K (500 °C), followed by HTA at 1973 K (1700 °C). The graphite edges were vertically oriented, but each domain was randomly rotated in the in-plane direction, which was confirmed via multiple cross-sectional transmission electron microscopy images obtained from different directions rotated 2, 5, 10, and 15° around the [001] axis. The Raman and photoluminescence exhibited no significant peaks. The initial sp2 structure state of the VEG was nucleated in an early stage of the HTA and the surface diamond was subsequently reconstructed, which was confirmed using stopping-and-range-of-ions-in-matter calculations and Rutherford backscattering/channeling (RBS-C) measurements. The RBS-C spectra indicate that the crystal is maintained after hot implantation and is recovered by HTA. This VEG structure may be useful for ohmic contact with diamond electrical devices. [ABSTRACT FROM AUTHOR]

A transparent polycrystalline diamond field-effect transistor (FET) was fabricated and measured in room temperature measurements, which reveals comparatively high maximum current density and high breakdown voltage of more than 1000 V. A harsh stress environment is proposed for simple and time-effective reliability stress measurement of the FET using a method of 50 continuous cycles of 500-V voltage stress. A 400-nm-thick Al2O3 counter-destructive passivation layer was implemented on the FET for the stress measurements. Devices with wide gate–drain length ( L_\text GD ) retain their FET characteristics after the harsh stress measurements by only 50% reductions maximum current density. [ABSTRACT FROM AUTHOR]

We evaluate and compare the performance and potential of GaAs and of wide and extreme bandgap semiconductors (SiC, GaN, Ga2O3, and diamond), relative to silicon, for power electronics applications. We examine their device structures and associated materials/process technologies and selectively review the recent experimental demonstrations of high voltage power devices and IC structures of these semiconductors. We discuss the technical obstacles that still need to be addressed and overcome before large-scale commercialization commences. [ABSTRACT FROM AUTHOR]

Diamond has unique physical properties, which show great promise for applications in the next generation power devices. Hydrogen-terminated (C–H) diamond metal–oxide–semiconductor field-effect transistors (MOSFETs) often have normally-on operation in devices, because the C–H channel features a p-type inversion layer; however, normally-off devices are preferable in power MOSFETs from the viewpoint of fail safety. We fabricated hydrogen-terminated (C–H) diamond MOSFETs using a partially oxidized (partial C–O) channel. The fabricated MOSFETs showed a high breakdown voltage of over 2 kV at room temperature and normally-off characteristics with a gate threshold voltage \textV\mathrm{th} of −2.5–−4 V. [ABSTRACT FROM PUBLISHER]

Hydrogen termination of diamond lowers its ionization energy, driving electron transfer from the valence band into an adsorbed water layer or to a strong molecular acceptor. This gives rise to p-type surface conductivity with holes confined to a subsurface layer of a few nanometers thickness. The transfer doping mechanism, the electronic behavior of the resulting hole accumulation layer, and the development of robust field-effect transistor (FET) devices using this platform are reviewed. An alternative method of modulating the hole carrier density has been developed based upon an electrolyte-gate architecture. The operation of the resulting “solution-gated” FET architecture in two contemporary applications will be described: the charge state control of nitrogen-vacancy centers in diamond and biosensing. Despite 25 years of work in this area, our knowledge of surface conductivity of diamond continues to develop. [ABSTRACT FROM PUBLISHER]

Applying the hydrogen (H) radical exposure at the last step of MOSFET fabrication process, an oxygen (O)-terminated channel was converted to a H-terminated one to obtain subsurface hole accumulation for field-effect transistor operation. Low-resistive titanium carbide (TiC) source/drain and alumina gate oxide were resistant to the hydrogenation process. The shallow TiC side contacts (~3 nm in depth) to the hole accumulation layer (channel) showed good ohmic contacts with a specific contact resistance of 2 x 10-7-7 x 10-7 Ω · cm². For diamond MOSFETs with the TiC ohmic layer, the saturated maximum drain current and maximum transconductance reached 160 mA/mm and 45 mS/mm, respectively. An fT of 6.2 GHz and an fmax of 12.6 GHz were obtained. The hydrogenation-last approach is a nondestructive method for the fabrication of diamond MOSFET with high production yield. [ABSTRACT FROM AUTHOR]

Submicrometer-gate (0.2-0.5-µm) diamond metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated on an H-terminated diamond surface. The maximum transconductance in dc mode reaches 165 mS/mm, while the average transconductance is 70 mS/mm in submicrometer-gate diamond MISFETs. The highest cutoff frequency of 23 GHz and the maximum frequency of oscillation of 25 GHz are realized in the 0.2-µm-gate diamond MISFET. From the intrinsic transconductances or the cutoff frequencies, the saturation velocities are estimated to be 4 × 106 cm/s in the submicrometer-gate FETs. They are reduced by gate-drain capacitance and source resistance. [ABSTRACT FROM AUTHOR]

The nitrogen vacancy (NV) center in diamond is fascinating and has a long spin coherence time. It is applied to magnetic sensors with high sensitivity (∼fT). To achieve a high sensitivity, an aligned NV ensemble is required. This paper presents a new methodology for the fabrication of two-dimensional (2D) aligned NV ensembles by using nitrogen-terminated (111) surface. To realize this, pure diamond growth and high nitrogen coverage on (111) surface were performed. As a result, we have succeeded in producing 2D NV ensembles, with 1 × 109 cm−2. Coherence time T 2 was 2.45 μs. Also, Using dynamical decoupling, the decoherence sources were revealed. The alignment ratio along [111] axis was archived 60%. Thermal annealing of the nitrogen termination was introduced to improve the alignment ratio. After that, the alignment rate was up to 73%. This report shows that the aligned 2D NV ensemble has possibility to be applied for multiple quantum devices. [Display omitted] • 2D aligned nitrogen vacancy ensembles created using nitrogen-terminated (111) surface. • Pure diamond growth and high nitrogen coverage were used. • The method afforded highly aligned nitrogen vacancy centers. • This technique enables nitrogen vacancy centers with multiple quantum application. [ABSTRACT FROM AUTHOR]

A C–Si bonded SiO 2 /diamond interface is formed under a SiO 2 mask during the selective diamond growth at a high temperature in a H 2 atmosphere including methane (5%). A few monolayers with C–Si bonding at the SiO 2 /diamond surface are confirmed through X-ray photoelectron spectroscopy at the C1s and Si2p core levels from 290 eV to 271 eV and 107 eV–95 eV, respectively. In addition, secondary ion mass spectroscopy results suggest that the C–Si bonds, and not C–H bonds, are majority at the interface and are mainly responsible for the field effect transistor (FET) operation. Two-dimensional hole gas C–Si diamond metal–oxide–semiconductor FET (MOSFETs) are fabricated using the C–Si diamond sub-surface as a p-channel. The MOSFETs in which the actual length from the source to the drain (L SD) is 12 μm–6 μm show appreciable field-effect mobility (e.g. 140 cm2V−1s−1 at L SD = 12 μm and 300 K) and normally-off operation. The wide temperature characteristics of the C–Si MOSFETs are confirmed and the device shows high stability, and a high on/off ratio of 106 is maintained at 673 K. The C–Si bonding at the SiO 2 /diamond interface provide a lower interface state density which makes the MOSFET show high drain current density and field-effect mobility with normally-off operation. Image 1 • A few monolayers with C–Si bonds are formed on a diamond surface at a high temperature in a reducing gas atmosphere. • The C–Si dipole like C–H dipole is expected to induce the accumulation of a two-dimensional hole gas under an electric field, which can be used as a p-channel to fabricate MOSFETs. • The heavily-boron-doped (p+) selectively grown diamond enhances the performance of the C–Si diamond MOSFET. • The C–Si diamond MOSFET shows excellent field-effect mobility (140 cm2V−1s−1) and normally-off operation. • The C–Si diamond MOSFET with the SiO 2 gate insulator shows a high on/off ratio of 106 is maintained at 673 K. [ABSTRACT FROM AUTHOR]

We fabricated (001) vertical diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with oxidized Si-terminated (C–Si–O) diamond channels on the surfaces and trench sidewalls. The C–Si–O diamond surface is approximately 1.0 eV weaker in negative electron affinity than the hydrogen-terminated (C–H) diamond surface, resulting in a smaller valence band bending between the interface of C–Si–O diamond surface and Al 2 O 3 , and larger the difference between the energy values of the fermi level and the valence band on the top (E F − E V), and the threshold voltage (V th) shifts in the negative direction. As a result, the maximum drain current density was 108 mA/mm, the V th was −9.0 V. Compared with conventional vertical diamond FETs using a C–H channel, the V th was shifted more than 20 V in the negative direction to reach normally-off mode. The normally-off operation was achieved while maintaining high current density, which is the first case of normally-off operation that has been observed in vertical diamond FETs. In, addition, it was confirmed that the diode functions as a freewheeling diode by adding a reverse drain voltage and allowing current to flow, and the change of current-voltage characteristics was also investigated by swapping the source and drain positions and performing measurements. [Display omitted] • P-channel vertical diamond MOSFETs are essential to realize high-power high-speed complementary inverters. • The 2DHG can be induced independent of the surface orientation. • Oxidized Si-terminated (C–Si–O) diamond surface can achieve normally-off operation at high drain current density. • High current density of 108 mA/mm and normally-off operation of −9.0 V were obtained. [ABSTRACT FROM AUTHOR]

In an attempt to fabricate an n-type Al 0.6 Ga 0.4 N film on a p-type diamond (111) substrate, the technique of remote N-plasma assisted MBE was used. Thin AlN layers were grown on boron-doped p-type diamonds to examine band alignment. Al 0.6 Ga 0.4 N layers were grown on the AlN layer. The techniques of RHEED, AFM, XPS, XPD, and Hall-measurements were used for the characterization. It was found that the AlN layers are not pure wurtzite but mixed possibly with amorphous Al 2 O 3 region and that the band alignments are favorably modified by the presence of possible amorphous Al 2 O 3. It was further found that the presence of ∼1ML of Si on the substrate diamond surface gives nearly type-I band alignment of amorphous Al 2 O 3 to the substrate. The Al 0.6 Ga 0.4 N layers were found in a form of ∼2 nm size grains surrounded possibly by amorphous Al 2 O 3 /Ga 2 O 3 regions. The Al 0.6 Ga 0.4 N layers were found to be n-type conductive with a very low mobility and the conductivity seems to be derived by thin metallic layers that possibly surrounding Al 0.6 Ga 0.4 N grains. [Display omitted] • In an attempt to fabricate an n-type Al 0.6 Ga 0.4 N/AlN layers on p-type diamond(111), remote N-plasma assisted MBE was used. • The AlN layers are not pure wurtzite but mixed with amorphous Al 2 O 3 region. • 1ML of Si on the substrate diamond surface gives favorable type-I band alignment of 'a-Al 2 O 3 '. • The Al 0.6 Ga 0.4 N layers are in the form of grains of ∼2 nm size surrounded by a-Al 2 O 3 /Ga 2 O 3 regions. • The conductivity of the Al 0.6 Ga 0.4 N layers is derived by Al and/or Al/Ga alloy layers that surround Al 0.6 Ga 0.4 N grains. [ABSTRACT FROM AUTHOR]

Lift-off is a promising method to prepare thin, high-finish, and freestanding large-area single crystal and polycrystalline diamonds. However, accurate control of the damage layer characteristic to achieve both stress release and lift-off process is difficult. In this work, high-energy C+ was implanted in single crystal diamond and polycrystalline diamond to create subsurface damage. The defect behavior and structural transformation of the ion implantation and annealing process were investigated. The homoepitaxial growth was subsequently carried out and the epitaxial layer was lifted off from the substrate by selectively etching the damaged layer. The results show that the cap layer and the substrate (below the damage layer) keep the sp3 carbon structure before and after annealing, which is confirmed by the atomic-scale electron energy loss spectroscopy (EELS). The high-resolution transmission electron microscopy (HRTEM) images show that after annealing at 1000 °C for 1 h, the damaged layer was transformed from amorphous carbon to a mixture of graphite and amorphous carbon, providing the damaged layer that could be removed by electrochemical solution. Meanwhile, the distorted diamond area was changed to a sharp interface, which ensures the low roughness of the substrate surface after the lift-off process. After etching for 30 h, a freestanding polycrystalline diamond film with a thickness of 100 μm and a surface roughness of 1.68 nm was obtained. The roughness of the lift-off substrate surface is 1.10 nm, indicating the epitaxial growth can be repeated directly without polishing. [Display omitted] • The defect behavior and structural transformation of the high-energy C+ implanted diamonds were investigated. • The stress state of the diamonds before and after ion implantation and after lift-off process were evaluated. • A 100 μm-thick freestanding polycrystalline diamond film with a surface roughness of 1.68 nm was successful obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high channel hole mobility of 200 cm2V−1s−1 was achieved in C-Si interface (1 1 1) diamond MOSFETs. • The C-Si interface provides the MOSFETs with an excellent normally-off operation. • The advantage of boron doping in (1 1 1) diamond provides a large maximum current density. • The anatomically flat and strain-free interface between the (1 1 1) diamond and SiO 2 film was confirmed by HRTEM. • The existence of C-Si bonds at the interface was proved by EELS and XPS. In this paper, a diamond-silicon (C-Si) interface was constructed on a (1 1 1) diamond substrate by annealing the SiO 2 gate insulator in a reductive atmosphere. Corresponding metal-oxide-semiconductor field effect transistors (MOSFETs) with a C-Si conductive channel were fabricated. The MOSFETs demonstrate excellent normally-off operation with a high threshold voltage (V th) of −16 V and a high current density of −167 mA/mm, with a gate length (L G) of 4 μm. The channel hole mobility (μ FE) reaches 200 cm2V−1s−1 with a L G of 10 μm, and the interface state density (D it) is as low as 3.8 × 1011 cm−2 eV−1. The high-resolution transmission electron microscopy (HRTEM) image displays a coherent and strain-free interface between the SiO 2 film and (1 1 1) diamond, which ensures a high μ FE and low D it in the MOSFETs. The interface is dominated by C-Si bonds, which are confirmed by atomic-scale electron energy loss (EELS) quantification, spectroscopic characterization, and X-ray photoelectron spectroscopy (XPS). These results demonstrate that diamond, directly combined with SiO 2 , is ideal for implementation in power devices. [ABSTRACT FROM AUTHOR]

Abstract: We have introduced pH sensors fabricated on diamond thin films through modification of the surface-terminated atom. We directly modified the diamond surface from hydrogen to amine or oxygen with ultraviolet (UV) irradiation under ammonia gas. The quantified amine site based on the spectra obtained by X-ray photoelectron spectroscopy (XPS) is 26% (2.6×1014 cm−2) with UV irradiation for 8h and its coverage is dependent on the UV irradiation time. This directly aminated diamond surface is stable with long-term exposure in air and electrolyte solution. We fabricated diamond solution-gate field-effect transistors (SGFETs) without insulating layers on the channel surface. These diamond SGFETs with amine modified by direct amination are sensitive to pH (45mV/pH) over a wide range from pH 2 to 12 and their sensitivity is dependent on the density of binding sites corresponding to UV irradiation time on the channel surface. [Copyright &y& Elsevier]

Abstract: The surface potential difference between an H-terminated surface and a locally oxidized diamond surface produced by an atomic force microprobe was investigated using a Kelvin probe force microscope. The potential of the H-terminated diamond surface was observed to be ∼0.1V higher than that of the oxidized diamond surface. The surface potential difference can be interpreted in terms of the positions of the vacuum level, the Fermi level, and the conduction and valence band edges, when negative electron affinity and p-type surface conduction are assumed on the H-terminated diamond surface. The surface dipole induced by the electronegativity differences between the surface atoms of the diamond affects the difference in the surface potential between the two surfaces. [Copyright &y& Elsevier]

Diamond field-effect transistors (FETs) whose channel is partially oxidized and highly resistive are fabricated by ozone treatment. These FETs are operated in electrolyte solutions. From XPS analyses, it is evident that hydrogen-terminated (H-terminated) diamond is partially oxygen-terminated (O-terminated) by ozone treatment. The quantification of surface oxygen in ozone-treated diamond is carried out. The quantification shows that the surface oxygen increases with an increase in ozone treatment time indicating the control of oxygen coverage. The partially O-terminated diamond surface channel is much less conductive compared with the H-terminated diamond. The ozone-treated FETs were operated stably even though the channel of the FETs becomes highly resistive. For the sensing of particular ions or molecules by the immobilization of sensing components, the control of surface termination is necessary. [Copyright &y& Elsevier]

Initial growth of heteroepitaxial diamond on Ir (0 0 1)/MgO (0 0 1) was investigated by scanning electron microscopy, reflection high-energy electron diffraction (RHEED) and atomic force microscopy. Bias-enhanced nucleation (BEN) was performed by antenna-edge-type microwave plasma assisted chemical vapor deposition. In BEN, diamond crystallites nucleated and grew along the [−1 1 0] and [1 1 0] directions of iridium. Diamond was likely to nucleate on protruded iridium areas. After BEN, in addition to the diamond diffraction spots, iridium bulk diffraction spots, which were not observed before BEN, were observed by RHEED. The iridium surface appeared to be protruded and changed by the high ion current density in BEN. Under [0 0 1] selective growth conditions, diamond crystallites, which were less than 10 nm in diameter, were etched by H2 plasma. Diamond nucleated areas corresponded to the surface ridges of iridium along the [−1 1 0] and [1 1 0] directions at 10–40 nm intervals before BEN. [Copyright &y& Elsevier]

Diamond heteroepitaxial thin films were successfully synthesized on high-quality Ir(001)/MgO(001) substrates. In bias-enhanced nucleation, antenna-edge-type microwave plasma-assisted chemical vapor deposition (MPCVD) was used. Subsequently, the 〈001〉 selective and smoothing growth processes were conducted by conventional MPCVD. Reconstructed (2×1) structure patterns have been observed by reflection high-energy electron diffraction (RHEED), which indicated that the surface of the diamond film is very smooth. The mean roughness is less than 2 nm in a 10-μm2 area, as revealed by atomic force microscopy observations. [Copyright &y& Elsevier]

A 0.7-μm-gate-length metal–insulator–semiconductor field effect transistor (MISFET) was fabricated on a hydrogen-terminated diamond surface conductive layer. The maximum transconductance of 100 mS/mm was obtained by DC measurement. The cut-off frequency of 11 GHz and the maximum frequency of oscillation of 18 GHz were achieved for the fabricated MISFET biased at VGS=0 V and VDS=−12 V. These are the highest values for diamond MISFETs ever reported. In the MISFET, high-frequency small-signal equivalent circuit analysis is carried out at VGS=0 V and VDS=−3, −5, −8, −10 and −12 V. The analysis indicates that the reduction of parasitic resistance between the source and gate is necessary for realizing higher output power. [Copyright &y& Elsevier]