Stephen E. Tetlak

Enhancement-mode Ga2O3 wrap-gate fin field-effect transistors on native (100) β-Ga2O3 substrate with high breakdown voltage

Sn-doped gallium oxide (Ga2O3) wrap-gate fin-array field-effect transistors (finFETs) were formed by top-down BCl3 plasma etching on a native semi-insulating Mg-doped (100) β-Ga2O3 substrate. The fin channels have a triangular cross-section and are approximately 300 nm wide and 200 nm tall. FinFETs, with 20 nm Al2O3 gate dielectric and ∼2 μm wrap-gate, demonstrate normally-off operation with a threshold voltage between 0 and +1 V during high-voltage operation. The ION/IOFF ratio is greater than 105 and is mainly limited by high on-resistance that can be significantly improved. At VG = 0, a finFET with 21 μm gate-drain spacing achieved a three-terminal breakdown voltage exceeding 600 V without a field-plate.

Dependence on proton energy of degradation of AlGaN/GaN high electron mobility transistors

The effects of proton irradiation energy on dc, small signal, and large signal rf characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. AlGaN/GaN HEMTs were irradiated with protons at fixed fluence of 5 × 1015/cm2 and energies of 5, 10, and 15 MeV. Both dc and rf characteristics revealed more degradation at lower irradiation energy, with reductions of maximum transconductance of 11%, 22%, and 38%, and decreases in drain saturation current of 10%, 24%, and 46% for HEMTs exposed to 15, 10, and 5 MeV protons, respectively. The increase in device degradation with decreasing proton energy is due to the increase in linear energy transfer and corresponding increase in nonionizing energy loss with decreasing proton energy in the active region of the HEMTs. After irradiation, both subthreshold drain leakage current and reverse gate current decreased more than 1 order of magnitude for all samples. The carrier removal rate was in the range 121–336 cm−1 over the range of proton energies employed in this study.

Implementation of High-Power-Density

A GaN high electron mobility transistor monolithic microwave integrated circuit (MMIC) designer typically has to choose a device design either for high-gain millimeter-wave operation with a short gate length, or for high-power-density X-band operation with a much larger gate/field-plate structure. We provide the designer the option of incorporating two different devices by implementing a 0.14-μm gate length GaN MMIC process capable of high-efficiency Ka-band operation while simultaneously achieving high power density in the same process flow. The key process enabler simply uses the capacitor top plate in the MMIC process as a field plate on the passivation layer. On two separate devices on the same chip using the same MMIC process flow, we demonstrate 7.7 W/mm at 35 GHz and VDS = 30 V on a standard 4 × 65-μm T-gated FET and then 12.5 W/mm at 10 GHz and VDS = 60 V on a 4 × 75-μm T-gated FET by adding a field plate. These are the highest reported power densities achieved simultaneously at X-band and Ka-band in a single wideband GaN MMIC process.

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Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O3 and (0001) Al2O3 substrates. Films deposited on β-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline β-Ga2O3 with a preferred (20 1 ¯ ) orientation. An average conductivity of 732 S cm−1 with a mobility of 26.5 cm2 V−1 s−1 and a carrier concentration of 1.74 × 1020 cm−3 was achieved for films deposited at 550 °C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices.

-Band AlGaN/GaN High Electron Mobility Transistors in a Millimeter-Wave Monolithic Microwave Integrated Circuit Process

Disordered ionic-bonded transition metal oxide thin-film transistors (TFTs) show promise for a variety of dc and RF switching applications, especially those that can leverage their low-temperature, substrate-agnostic process integration potential. In this paper, enhancement-mode zinc-oxide TFTs were fabricated and their switching performance evaluated. These TFTs exhibit the drain-current density of 0.6 A/mm and minimal frequency dispersion, as evidenced by dynamic current-voltage tests. A high-frequency power switch figure of merit RONQG of 359 mQ · nC was experimentally determined for 0.75-μm long-channel devices, and through scaling 45.9 mQ · nC is achievable for 11 V-rated devices (where RON is ON-state drain-source resistance, and QG is gate charge). An RF switch cutoff frequency fc of 25 GHz was measured for the same 0.75-μm TFT, whereas fc exceeding 500 GHz and power handling in the tens of watts are projected with optimization.

Highly conductive homoepitaxial Si-doped Ga2O3 films on (010) β-Ga2O3 by pulsed laser deposition

Summary form only given. In this work, we characterize the scalability of ZnO TFTs for RF transistor and DC switching applications through variations in channel length, total device periphery, and parasitic gate overlap capacitance. For simple device test structures that have not been optimized for either RF transistors or DC switches, we show drain current density (I_DS) and R_on scalability for channel lengths (L_C) from 10 μm down to 150 nm achieving I_DS = 840 mA/mm. Separately, R_on·Q_G values as low as 359 mΩ-nC were measured for devices with mobility (μ_e) = 28 cm²/V·s and contact resistance (ρ_c) = 1 Ω·mm. R_on·Q_G values were observed to scale well for total device peripheries (W) ranging from 50 μm to 2 mm. Significant improvements in I_DS, Ron, and R_on·Q_G are projected through ohmic contact and mobility optimization, as well as parasitic gate overlap capacitance scaling.

Ionic Metal–Oxide TFTs for Integrated Switching Applications

Recently, β-Ga2O3 FETs have been introduced [1]-[3] as potential devices for high power, switching, and RF applications with increased performance and more cost effective means of production when compared to GaN or SiC. Documented material properties leading to a Baliga [4] figure of merit nearly four times that of GaN [1], indicate potential for reduced specific on resistance at higher breakdown voltages if theoretical material characteristics can be exploited. To achieve projections, however, low thermal conductivity of ~13 W/mK [5] [6], less than a tenth of GaN or SiC [7], must be managed. We present electrical characterization for ß-Ga2O3 MOSFETs using both static and pulsed measurement systems. Our results show the extent of thermal effects and provide a basis for developing test protocols to effectively characterize the devices without inducing thermal effects or degradation.