AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using electron-beam evaporated high-dielectric-constant (high- k ) lanthanum oxide layer (normalLa2normalO3) as the gate insulator have been investigated and compared with the traditional GaN HEMTs. The dielectric constant of the normalLa2normalO3 insulator layer developed in this study was 13.1. In addition, a negligible hysteresis voltage shift in the capacitance–voltage curves can be obtained after high temperature annealing. The compositions and the crystalline structures of normalLa2normalO3 with different annealing temperatures were observed by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. The normalLa2normalO3 thin film achieved a good thermal stability after 200, 400, and 600°C postdeposition annealing owing to its high binding energy (835.7eV) characteristics. Moreover, the gate leakage current of a traditional metal gate GaN HEMT can be suppressed for 1 order of magnitude after inserting a normalLa2normalO3 insulator between Ni and AlGaN, resulting in a better pulsed-mode operation. The device linearity was also improved due to its flat and wide transconductance (gnormalm) distribution, which was analyzed by a polynomial curve-fitting technique. Therefore, normalLa2normalO3 is a potential candidate high- k material for the gate insulator to enhance the GaN-based field effect transistor performance while scaling down the device dimension and device reliability at high power operation.
Gateless AlGaN/GaN high electron mobility transistors (HEMTs) has some advantages include rapid response, low noise, and superior sensitivity. In different Al content, the Al 0.3 Ga 0.7 N has the excellent performance among Al 0.17 Ga 0.83 N and Al 0.25 Ga 0.75 N, and the performance can be achieved about -0.923 mA/mm-pH during pH 4-10, and -2.24 mA/mm-pH during pH 7-8. The result indicates that the better performance of Al 0.3 Ga 0.7 N can be applied in high sensitivity pH sensor. Using the characteristic and modifying by different gate oxide, there are many application in the technology of medical for detecting the disease.
The properties of a GaAs enhancement-mode metal-oxide-semiconductor high electron mobility transistor ͑E-MOSHEMT͒ were demonstrated using an electron-beam deposited Pt/ZrO 2 composited gate structure. X-ray photoelectron spectroscopy was conducted to measure the binding energies of ZrO 2 thin films with various postannealing temperatures, and its structural properties remained stable up to 600°C. A 20 nm thick Pt metal layer between AlGaAs and ZrO 2 was used as a buried metal to control the device threshold voltage ͑V th ͒ for the enhancement-mode operation. By calculating the capacitance-voltage ͑C-V͒ measured curves, the dielectric constant of ZrO 2 was 12.6 and the voltage shift of the C-V hysteresis phenomena can be reduced to 4.5 mV after 400°C postannealing. Measured load-pull power results have also shown that ZrO 2 E-MOSHEMT achieved a better power added efficiency at a high input swing owing to the gate leakage current reduction. The electron-beam evaporated Pt/ZrO 2 /Ti/Au composited gate MOSHEMT is suitable for high volume production due to its in situ insulator and metal gate deposition in the same chamber.GaAs-based enhancement-mode pseudomorphic high electron mobility transistors ͑E-pHEMTs͒ have recently attracted tremendous attention for microwave power amplifier applications because of their high power added efficiency ͑PAE͒ and single voltage supply characteristics. To obtain an enhancement-mode ͑E-mode͒ operation of pHEMTs, Pt gate was sunk into the AlGaAs barrier layer to form a metallic alloy. The sinking of Pt into the barrier shifted the gate metal front closer to the InGaAs channel to guarantee an extreme low drain leakage current at zero gate bias. However, a serious gate leakage current and a small gate voltage swing region still limit the device performance under high input power operation. Therefore, the device electrical performance can be improved significantly by inserting a high quality and high dielectric constant ͑high-k͒ insulator layer between the metal gate electrode and the AlGaAs barrier layer to form the metal-oxide-semiconductor ͑MOS͒ architecture. [1][2][3] In this regard, we developed an enhancement-mode metal-oxidesemiconductor high electron mobility transistor ͑E-MOSHEMT͒ by using the electron-beam deposited Pt/ZrO 2 /Ti/Au composited gate structure. Because the metals ͑Ti/Au͒ above ZrO 2 were identical to the previous Schottky gate design, the gate resistances for both devices were similar. For the GaAs MOSHEMT development, a high dielectric constant oxide layer is a key factor to suppress the device gate leakage current together with a good channel modulation ability. In addition, power devices consumed huge amount of power, and in consequence a huge amount of heat was generated during operation. Therefore, a thermally stable high-k oxide insulator is also important. Among the various high-k dielectrics studied, ZrO 2 is a promising candidate for gate dielectrics because ZrO 2 exhibited a large bandgap ͑5.2-7.8 eV͒, a relatively high dielectric constant ͑Ͼ25͒, and a h...
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