Yu Hao Chang

Herein, excellent electrical performances were achieved for the oxidized-silicon-terminated diamond (C-Si-O) metal-oxide-semiconductor field-effect transistors (MOSFETs) using chemical-vapor deposition-grown SiO ₂ as the filling insulator of shallow-trench-isolation (STI) structures and gate oxide. The C-Si-O interface was formed under the initial SiO ₂ layer (1 ^st SiO ₂ ) as a mask during heavily boron-doping growth. The surface carbon-rich layer formed on the mask during selective diamond regrowth was removed using the oxygen plasma ashing treatment. The device having a 130-nm-thick SiO ₂ gate insulator exhibited subthreshold slopes ( SS ) of 220-710 mV/dec between 473 and 673 K. A normally-off operation was confirmed at 673 K. The filling insulator (2 ^nd SiO ₂ ) containing positive fixed charges can block the hole transport channels and the active regions of the device are out of one plane using the STI structures. Accordingly, OFF-state drain leakage current was successfully suppressed. Consequently, high on-off ratios of 10 ⁶ -10 ⁷ that cannot be realized in hydrogen-terminated (C-H) diamond FETs were confirmed up to 673 K. To summarize, results of this study provide new strategies for advancing diamond devices from the laboratory to industrial applications.

An all-solid-state pH sensing system utilizing a stainless steel vessel (SUS304) and a pH-insensitive diamond solution-gate field-effect transistor (SGFET) is presented here to explain the interaction between stainless steel vessel and field-effect transistor (FET) pH sensors for the first time. A pH sensitive ion-sensitive field-effect transistor (ISFET) was first used to show the change of the sensing behavior from 47.78 mV/pH to -4.73 mV/pH when using an Ag/AgCl electrode and stainless steel vessel as the gate, respectively. This intriguing sensing behavior was investigated by developing large and small-signal equivalent circuit models in a transistor circuit for both the Ag/AgCl and the stainless steel vessel gate. The result shows that the targeted ion change ΔQ _h corresponding to the pH sensitivity has been offset which explains the phenomenon observed when using the pH sensitive ISFET with the stainless steel vessel. We then hypothesize that combining a pH insensitive device with the stainless steel vessel gate should show a pH sensitivity close to the Nernst response. To validate this, a pH insensitive diamond SGFET was then fabricated and combined with the stainless steel vessel for pH measurements. The system demonstrates a high pH sensitivity at -54.18 mV/pH across a wide range of pH solutions (pH 2-12) and remains stable in elevated temperatures when measured with a potentiostat setup at 80 °C. The results also suggest that this all-solid-state sensing system has great potential to be used in the food and beverage industry where stainless steel is widely employed due to its excellent corrosion resistance, low cost, and high sensing capabilities.

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 SiO ₂ masks with an atomic layer deposition (ALD)-Al ₂ O ₃ film as the main gate insulator was proposed for the first time. Compositional analysis across the SiO ₂ 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 SiO ₂ mask, a carbon-rich film was formed on SiO ₂ and C–Si bonding was realized at the SiO ₂ /(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-Al ₂ O ₃ 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.

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-Al ₂ O ₃ . 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.

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.

PH sensing facilitates many substantial aspects of the society such as chemical laboratory analysis, agriculture, or water and soil qualities. However, existing pH sensors have problems and limitations such as fragility, hysteresis, or slow responding time. In this research, a new method utilizing fluorocarbon thin film via fluorine termination and boron‐doped diamond (BDD) solution‐gate field‐effect transistors (SGFETs) for pH sensing is developed for the first time. The fluorocarbon film device demonstrates a high pH sensitivity of 67.4 and 34.9 mV pH⁻¹ in acid and alkaline pH regions, respectively.

ZrO₂ films were deposited on C-face 4H-SiC substrates by using an RF sputter at a temperature of 200°C. Then, ZrO₂ films were treated with RTA (rapid thermal annealing) process in Argon (Ar) ambient at 600°C, 700°C and 800°C for 4 minutes, respectively. The samples with RTA process show the lower leakage currents. As the measure temperature increases from room temperature (RT) to 150°C, the dielectric breakdown voltage reduces from 3 V to 1 V. The difference between quasi C-V characteristics and high frequency C-V characteristics at 1 MHz becomes larger with increasing RTA temperature. The C-V curves also shift to the left side as the measure temperature increases from RT to 150°C. It also shows the ledge on the C-V curves of samples with RTA at elevated measure temperature.

Using metalorganic chemical vapor deposition assisted by a nitrogen radical irradiation generated by rf plasma, we have enhanced the quality and the step coverage of titanium nitride barrier metals for the contact holes with a high aspect ratio and a submicron radius. Electrical resistivity measurements show that the film resistivity improves by a factor of five as the proper nitrogen irradiation has been applied. The step coverage in a contact hole with 0.4 μm diam and 3:1 aspect ratio has been improved from 50% to 80% by applying nitrogen plasma, clearly demonstrating the effectiveness of this technique in the conformal deposition of barrier metals for the ultra‐large scale integration. The incident nitrogen radical is believed to play several roles, such as the enhancement of surface migration rate of molecules and the reduction of the amount of hydrocarbon incorporating into the film during the deposition.