Characterization of AlGaN/GaN MISHFETs on a Si substrate by static and high-frequency measurements

Abstract

AlGaN/GaN/Si metal-insulator-semiconductor heterostructure field-effect transistors (MISHFETs) with SiN and Al 2 O 3 gate insulators are characterized by static and high-frequency measurements, and their performance is compared with nonpassivated and SiN-passivated heterostructure field-effect transistors (HFETs). The saturation drain current increased from ∼500 mA mm −1 for the HFETs to ∼770 mA mm −1 for the MISHFETs. The peak extrinsic transconductance of the MISHFETs (147 mS mm −1 for 8 nm SiN and 220 mS mm −1 for 4 nm Al 2 O 3 ) is higher than expected due to the increased gate-to-channel separation. Similarly, small signal microwave characterization yielded an increase in the current gain cut-off frequency (from 3.2 to 7.2 GHz) and the maximum frequency of oscillation (from 12.3 to 20.4 GHz) for the MISHFETs with 2 μm gate length compared to the HFET counterparts. Finally, the density of trap states, evaluated from the frequency-dependent conductance measurements, was ∼ =3 × 10 12 cm −2 eV −1 for the HFETs but only ∼ =1.8 × 10 12 cm −2 eV −1 for the MISHFETs. All of these demonstrate the capability of AlGaN/GaN MISHFETs of preparing high-performance and cost-effective devices for high-power microwave applications on a Si substrate.when compared with sapphire. Unfortunately, high-resistive SiC substrates are a costlier alternative to AlGaN/GaN devices. Devices on Si 8 , on the other hand, are the best solution considering their low cost, high crystalline perfection, good thermal conductivity and large-area availability of Si substrates.Recently, an excellent millimetre-wave performance (e.g. maximum frequency of oscillation of 110 GHz and noise figure of 1.3 dB at 20 GHz) has been reported on AlGaN/GaN-on-Si HFETs [1].

Preparation and properties of AlGaN/GaN MOS-HFETs with atomic layer deposited Al<inf>2</inf>O<inf>3</inf> as gate oxide

“…Values of n S = 6×10 12 and 7.25×10 12 cm -2 and V th = -3.7 and -4.6 V were obtained for the HFET and MOS-HFET, respectively. Higher n s on the MOS-structure indicate the passivation effect [11].…”

Preparation and Properties of GaN-Based MOSHFETs

“…A remarkable increase of the f T and f max values was found for Al 2 O 3 /AlGaN/GaN/Si MOSHFETs compared to the HFET counterparts. The peak f T and increased from 3.2 GHz for the HFETs to 9.6 GHz for the MOSHFETs (2 µm gate length) [9]. Consequently, the peak f max increased from 12.3 GHz for the HFETs to 20.4GHz for the MOSHFETs.…”

“…An example is shown in Fig. 2 [9]. This effect can be attributed to an increase of the carrier density n s and/or drift velocity v d , as I DS /W G = q⋅n s ⋅v d .…”

Comparison of AlGaN/GaN HFETs and MOSHFETs in prospect of oscillator design

“…Optimization of the cutoff frequency f t as well as the maximum oscillation frequency f max is a crucial point to achieve high RF performance for both applications. In this work we investigate AlGaN/GaN HFETs and also AlGaN/GaN metal-oxide-semiconductor HFETs (MOSHFETs) which are under systematic study for a short time [2]. Both the gate resistance R g and gate-drain capacitance C gd are determining a time constant W R g · C gd which influences the frequency of oscillation f max .…”