Tomohiro Murata

A high-power RF switch IC using AlGaN/GaN HFETs with single-stage configuration

A high-power single-pole double throw (SPDT) switch IC using AlGaN/GaN heterojunction field-effect transistors (HFETs) is demonstrated for the first time. The reduction of on-resistance (R/sub on/) and off-capacitance (C/sub off/) for AlGaN/GaN HFETs enables the GaN-based switch IC that can be applied for practical RF applications. A novel Si-doping technique is employed to reduce ohmic contact resistance, which successfully reduces the R/sub on/. The C/sub off/ of the HFETs on a sapphire substrate is found to be smaller than that on a SiC substrate, together with low cost fabrication. The GaN-based SPDT switch IC with single-stage configuration is designed by using a circuit simulator based on the extracted device parameters. The fabricated SPDT switch IC achieves insertion loss of 0.26 dB and isolation of 27 dB at 1 GHz, as well as an extremely high-power handling capability of 43 W. This value is 10 times higher than that of typical GaAs-based switch ICs. In addition, the switch IC exhibits low distortion characteristics, where the third-order intercept point of 41 dBm is achieved. The chip size is reduced to 40% as compared with conventional four stage GaAs-based switch ICs by using the single-stage circuit configuration.

AlN Passivation Over AlGaN/GaN HFETs for Surface Heat Spreading

Reduction of thermal resistance in AlGaN/GaN heterojunction field-effect transistors (HFETs) is critical for further increase in their output power to be handled in these promising material systems. In this paper, we present a new technique to reduce it using polycrystalline AlN passivation deposited by dc sputtering as a surface heat spreader over AlGaN/GaN HFETs. The AlN is deposited by dc sputtering, and it is well oriented to the c-axis. The measured thermal resistances of AlGaN/GaN HFETs with AlN passivation are lower than those with SiN passivation, which well agree with the results of the thermal simulation. The most notable change of the characteristics by AlN passivation is that the drain current increases by 30%, and the on-state resistance is reduced by 66% by the passivation; moreover, the current collapse suppresses successfully. As a result, the radio frequency output power is higher than that with conventional SiN passivation and is increased by increasing the thickness of AlN passivation. Thus, reduction of the thermal resistance and higher output power by AlN passivation is experimentally achieved.

Source resistance reduction of AlGaN-GaN HFETs with novel superlattice cap layer

We have developed a novel AlGaN-GaN heterojunction field effect transistor (HFET) with an ultralow source resistance by employing the novel superlattice (SL) cap structure. The particular advantage of the SL cap, i.e., the existence of multiple layers of the polarization-induced two-dimensional electron gas (2DEG) with high mobility and high concentration at each AlGaN-GaN interface, is fully exploited for lowering the lateral resistance and the potential barrier at the interface of the SL cap and the HFET barrier layer. By designing the AlGaN-GaN thickness ratio, we have established a method to obtain the optimized SL structure and have achieved an extremely low source resistance of 0.4 /spl Omega//spl middot/mm which is lower not only than HFETs with the conventional structure but also than those with the n-GaN cap structure. The SL cap HFET fabricated on a sapphire substrate exhibited excellent dc and RF performance, i.e., maximum transconductance of over 400 mS/mm, maximum drain current of 1.2 A/mm, a cutoff frequency of 60 GHz, a maximum frequency of oscillation of 140 GHz, and a very low noise figure minimum of 0.7 dB at 12 GHz.

19.7 A 79GHz binary phase-modulated continuous-wave radar transceiver with TX-to-RX spillover cancellation in 28nm CMOS

The demand for inexpensive and ubiquitous accurate motion-detection sensors for road safety, smart homes and robotics justifies the interest in single-chip mm-Wave radars: a high carrier frequency allows for a high angular resolution in a compact multi-antenna system and a wide bandwidth allows fora high depth resolution. With the objective of single-chip radar systems, CMOS is the natural candidate to replace SiGe as a leading technology [1-6].

A high power Tx/Rx switch IC using AlGaN/GaN HFETs

An extremely high power Tx/Rx switch IC based on AlGaN/GaN HFETs has been developed for the first time. A low on-state resistance realized by Si doping techniques and a low off-state capacitance by using an Al/sub 2/O/sub 3/ substrate led to excellent performance of 0.26 dB insertion loss and 27 dB isolation with the power handling capability of 43 W at 1 GHz.

AlGaN/GaN devices for future power switching systems

GaN/AlGaN device technologies are presented aiming at the applications to power switching systems. In order to reduce on-resistance (Ron), we developed SL (super lattice) capping and QA (quaternary alloy) over-layer techniques for GaN/AlGaN HFET. Further, we achieved almost the same mobility keeping the same 2DEG density for GaN/AlGaN hetero structure grown on Si (111) substrates, which will make the cost comparable to conventional Si one. The experimentally obtained RonA of the FET is 1.9 mOmegacm2, which is 14 times lower than that of Si ones. Additionally, a novel approach to realize enhancement-mode operation of GaN/AlGaN FET is examined over R-plane sapphire, where non-polar AlGaN/GaN heterostructure, free from polarization charge, can be grown

Experimental and theoretical examination of orientation effect on piezoelectric charge at gate periphery in AlGaN/GaN HFETs

Orientation effect on AlGaN/GaN heterojunction field-effect transistors (HFETs) has been experimentally and theoretically examined in detail. The drain-currents of the fabricated AlGaN/GaN HFETs with various gate directions do not depend on the gate orientation, whereas those of GaAs-based HFETs strongly depend on the gate direction due to the piezoelectric charges induced around the gate electrode. The piezoelectric charges induced in the vicinity of the gate electrode are simulated by using a finite-element method. This simulation solves the piezoelectric equations with piezoelectric and elastic stiffness constants, assuming that stress is applied to the gate edges in the HFET. The detailed simulation reveals that the piezoelectric charge distribution does not depend on the gate direction, although a large amount of piezoelectric charges is induced in the vicinity of the gate edges, which is consistent with the experimental result. Moreover, it is mathematically clarified that these experimental and simulated results are due to the symmetry characteristic of the piezoelectric and elastic stiffness constants for nitride semiconductor materials

GaN-based multi-junction diode with low reverse leakage current using P-type barrier controlling layer

We present a novel GaN-based diode with low reverse leakage current which ensures the high voltage operation up to 600V. The diode consists of multi-junctions of AlGaN/GaN with a p-GaN overlayer where the anode and cathode are formed on the sidewalls of the channels. The tunneling current which is the origin of the leakage current can be reduced by controlling the potential barrier at the anode sidewall by means of the depletion layer from the p-GaN. The fabricated GaN diode with the p-type barrier controlling layer (BCL) exhibits high forward current of 18A at 1.5V with the breakdown voltages over 600V taking advantages of the reduced leakage current. The fabricated GaN-based diode has smaller RonC of 70 pΩF than 95 pΩF of the commercially available SiC Schottky barrier diode (SBD) indicating that the GaN diode is suitable for power switching. The GaN diode exhibits high conversion efficiency of 98.2 % in the voltage boosting converter at the output voltage of 400V by combining it with a GaN Gate Injection Transistor (GIT). The obtained performance by using the GaN diode is superior to that with a SiC SBD.

High fmax with High Breakdown Voltage in AlGaN/GaN MIS-HFETs using In-Situ SiN as Gate Insulators

AlGaN/GaN heterojunction transistors (HFETs) with metal-insulator-semiconductor (MlS)-type gate structure is promising for high frequency and high power applications owing to the superior material properties together with the reduced gate leakage current. In this paper, we present a novel AlGaN/GaN MIS-HFET using so-called in-situ SiN as a gate insulator. The in-situ SiN with a crystalline structure is formed subsequently after the epitaxial growth in the same reactor without any exposure in the air. The formation of the in-situ SiN greatly enhanced the sheet carrier concentration, which helps the reduction of the parasitic resistances. The fabricated MIS- HFET exhibits very high maximum oscillation frequency (fmax) of 203 GHz for the device with the gate length of 100 nm. The device exhibits the off-state breakdown voltages of 190 V at highest maintaining the high fmax over 190 GHz, and is thus promising for high frequency and high power applications including future millimeter wave communication systems.

A K-band AlGaN/GaN HFET MMIC Amplifier on Sapphire using novel superlattice cap layer

We have developed a K-band AIGaN/GaN HFET MMIC amplifier by applying an AIGaN/GaN superlattice (SL) capped structure on sapphire substrate. Owing to the lowest (0.4 Ω. mm) source resistance of A1GaN/GaN HFETs, the HFETs exhibited excellent DC and RF characteristics, and sufficient ability to operate in the K-band frequency range is obtained. The fabricated MMIC with a CPW-line structure exhibited a small-signal gain higher than 10 dB with a 3-dB bandwidth of 20-24.5 GHz and that of 13 dB at 21.6GHz when biased at a supply voltage of 7 V. The 1dB compression point (P 1 d B ) referred to output of 15.4 dBm at 21.6 GHz was obtained. This work is the first report of MMIC amplifier fabricated on sapphire successfully operating in the K band.