Pulsed Large Signal RF Performance of Field-Plated Ga₂O₃ MOSFETs

Abstract

Comparison between pulsed and CW large signal RF performance of field-plated β-Ga 2 O 3 MOSFETs has been reported. Reduced self-heating when pulse resulted in a power added efficiency of 12%, drain efficiency of 22.4%, output power density of 0.13 W/mm, and maximum gain up to 4.8 dB at 1 GHz for a 2-μm gate length device. Increased power dissipation for higher V DS and I DS resulted in a degradation in performance, which, thermal simulation showed, could be entirely explained by self-heating. Buffer and surface trapping contributions have been evaluated using gate and drain lag measurements, showing minimal impact on device performance. These results suggest that β-Ga 2 O 3 is a good candidate for future RF applications. Index Terms-Ga 2 O 3 MOSFET, large signal RF, pulsed RF, power added efficiency (PAE), pulsed IV. I. INTRODUCTIONT HE material of β-Ga 2 O 3 with a bandgap of 4.9 eV and large electric breakdown strength of 8 MVcm −1 has garnered great interest in the power conversion community; however, there are also opportunities for RF applications [1], [2]. Ga 2 O 3 features a Baliga's figure of merit (BFOM), which is based on the mobility and bandgap, more than 10× higher than for SiC and 4× higher than for GaN [3]. High breakdown voltages up to 755 V with a high drain current on/off ratio of 10 9 have been demonstrated for lateral Ga 2 O 3 transistors [4]. Johnson's figure of merit (saturation velocity times critical electric field product, vsat•Ec) for high frequency devices is very much comparable to GaN [1], [5].

A novel β‐Ga2O3 HEMT with fT of 166 GHz and X‐band POUT of 2.91 W/mm

“…The higher f T peak of the BGO HEMT can be attributed to its substantially smaller gate capacitance C gg = 0.5 pF/mm (= 0.1 μF/cm −2 , when normalized on gate area) over delta-doped β-Ga 2 O 3 experimental FETs. 20 Along the same lines, the transconductance of the BGO HEMT (g m = 0.917 S/mm) is significantly larger than that of the latest reported experimental work. 21 However, we obtained a comparatively large output conductance (g ds ) of 866 mS/mm (at operating points relating to peak f T and f MAX ) over L G = 100 nm ( g ds = 0.428) for the same device structure.…”

“…The cut‐off frequency ( f T ) and maximum oscillation frequency ( f MAX ) are extracted to be 166 and 292 GHz respectively at which the respective gain decreases to unity (gain is reduced to 0 dB). The higher f T peak of the BGO HEMT can be attributed to its substantially smaller gate capacitance C gg = 0.5 pF/mm (= 0.1 μF/cm −2 , when normalized on gate area) over delta‐doped β ‐Ga 2 O 3 experimental FETs 20 . Along the same lines, the transconductance of the BGO HEMT ( g m = 0.917 S/mm) is significantly larger than that of the latest reported experimental work 21 .…”

“…A maximum power output efficiency of 14% is obtained, which is more than double that of 6.3%, 18 and slightly improved over 12%. 20 As shown in Figure 5, the estimated 2DEG sheet charge density in the proposed device is 5 × 10 13 /cm 2 . Since in the high carrier density and high-current regime, current increases as √ n s as predicted by optical phonon model 47 and so effective electron velocity v e decreases as 1= ffiffiffiffi ffi n s p as v e = ∂J/q∂n s , 47 which results in increased channel delay as intrinsic delay can be expressed as τ c = L g /v e .…”

“…As per recent reported β-Ga 2 O 3 FETs/MODFETs, maximum achievable 2DEG density is limited to 10 12 cm −2 . [14][15][16][17][18][19][20] On the other hand, the proposed device utilizes highly polarized AlN to induce high 2DEG density of 10 13 cm −2 .…”

“…16,17 Although, higher doped silicon delta-doped layer led to parasitic channels in the barrier layer. 17 Regarding RF performance of β-Ga 2 O 3 devices, β-Ga 2 O 3 MOSFETs (gate length L G = 3.8 μm) with current gain cut-off frequency (f T ) of 3.3 GHz, 18 BGO MOSFET (L G = 0.14 μm) with f T of 5 GHz, 19 improved power efficiency of 12% when using pulsed signal in field-plated β-Ga 2 O 3 MOSFET, 20 and deltadoped FETs (L G = 120 nm) with f T of 27 GHz 21 are reported. The gate length and device aspect ratio play a critical role in high frequency β-Ga 2 O 3 devices.…”