Hironobu Miyamoto

10-W/mm AlGaN-GaN HFET with a field modulating plate

AlGaN-GaN heterojunction field-effect transistors (HFETs) with a field modulating plate (FP) were fabricated on an SiC substrate. The gate-drain breakdown voltage (BV/sub gd/) was significantly improved by employing an FP electrode, and the highest BV/sub gd/ of 160 V was obtained with an FP length (L/sub FP/) of 1 /spl mu/m. The maximum drain current achieved was 750 mA/mm, together with negligibly small current collapse. A 1-mm-wide FP-FET (L/sub FP/=1 /spl mu/m) biased at a drain voltage of 65 V demonstrated a continuous wave saturated output power of 10.3 W with a linear gain of 18.0 dB and a power-added efficiency of 47.3% at 2 GHz. To our knowledge, the power density of 10.3 W/mm is the highest ever achieved for any FET of the same gate size.

A normally-off GaN FET with high threshold voltage uniformity using a novel piezo neutralization technique

In this paper, we successfully demonstrate a recessed gate normally-off GaN FET on a silicon substrate with high threshold voltage (V<inf>th</inf>) uniformity and low on-resistance. In order to realize high V<inf>th</inf> uniformity, a novel V<inf>th</inf> control technique is proposed, which we call “piezo neutralization technique”. This technique includes a piezo neutralization (PNT) layer formed at the bottom of the gate recess. Since the PNT layer neutralizes the polarization charges under the gate, the V<inf>th</inf> comes to be independent of the gate-to-channel span. The fabricated normally-off GaN FET with PNT structure exhibits an excellent V<inf>th</inf> uniformity (σ(V<inf>th</inf>)=18 mV) and a state-of-the-art combination of the specific on-resistance (R<inf>on</inf>A=500 mΩmm²) and the breakdown voltage (V<inf>B</inf>≫1000 V). The normally-off GaN FETs wtih PNT structure show great promise as power devices.

High-power recessed-gate AlGaN-GaN HFET with a field-modulating plate

Recessed-gate AlGaN-GaN heterojunction field-effect transistors (FETs) with a field-modulating plate (FP) have been successfully fabricated for high-voltage and high-power microwave applications. The developed recessed-gate FP-FET with a gate length of 1 /spl mu/m exhibited an increased transconductance of 200 mS/mm. A series of current collapse measurements revealed that the recessed-gate FP-FET is highly desirable for collapse-free high-voltage power operation. Equivalent circuit analysis demonstrated that the gain loss due to the additional gate feedback capacitance associated with the FP electrode is considerably compensated by increasing the drain bias voltage to more than 30 V. A 48-mm-wide recessed-gate FP-FET biased at a drain voltage of 48 V exhibited a record saturated output power of 197 W with a linear gain of 10.1 dB and a power-added efficiency of 67% at 2 GHz.

30-GHz-band over 5-W power performance of short-channel AlGaN/GaN heterojunction FETs

This paper describes the small-signal characterization through delay-time analysis and high-power operation of the Ka-band of AlGaN/GaN heterojunction field-effect transistors (FETs). An FET with a gatewidth of 100 /spl mu/m and a gate length of 0.09 /spl mu/m has exhibited a current gain cutoff frequency (f/sub T/) of 81 GHz, a maximum frequency of oscillation (fmax) of 187 GHz, and a maximum stable gain of 10.5 dB at 30 GHz (8.3 dB at 60 GHz). Delay-time analysis has demonstrated channel electron velocities of 1.50/spl times/10/sup 7/ to 1.75/spl times/10/sup 7/ cm/s in a gate-length range of 0.09-0.25 /spl mu/m. State-of-the-art performance-saturated power of 5.8 W with a linear gain of 9.2 dB and a power-added efficiency of 43.2%-has been achieved at 30 GHz using a single chip having a gatewidth of 1.0 mm and a gate length of 0.25 /spl mu/m.

A 110-W AlGaN/GaN heterojunction FET on thinned sapphire substrate

SiN-passivated AlGaN/GaN heterojunction FETs (HJFETs) were fabricated on a thinned sapphire substrate. A 16 mm-wide HJFET on a 50 /spl mu/m-thick sapphire exhibited 22.6 W (1.4 W/mm) CW power, 41.9% PAE, and 9.4 dB linear gain at 26 V drain bias. Also, a 32 mm-wide device, measured under pulsed operation, demonstrated 113 W (3.5 W/mm) pulsed power at 40 V drain bias. To our best knowledge, 113 W total power is the highest achieved for GaN on any substrate, establishing the validity of the GaN-on-thinned-sapphire technology.

Novel AlGaN/GaN dual-field-plate FET with high gain, increased linearity and stability

We have successfully developed a novel AlGaN/GaN FET with dual field-modulating-plates (FPs). The breakdown voltage is enhanced from 125 to 250 V by adding the second FP to the conventional FP structure. Benefiting from the first FP, no current collapse is observed simultaneously. Since the second FP effectively reduces feedback capacitance, this device provides a 3-dB higher gain along with increased linearity and stability. Under a 2.15-GHz W-CDMA modulation scheme, a dual-FP-FET with a 24-mm gate periphery achieved a state-of-the-art combination of 160-W output power and a 17.5-dB linear gain

16 Mbit SRAM cell technologies for 2.0 V operation

Novel memory cell technologies for 2.0-V cell operation of 16-Mb SRAMs (static RAMs) have been developed. These technologies have realized 7.2- mu m/sup 2/ cell size, 4.4 effective cell ratio for high noise immunity, and 10/sup 13/-A/cell leakage current. The key features of these technologies include: (1) a symmetrical cell configuration; (2) an access transistor with an N/sup -/ offset resistor; (3) a ground plate expanded on the cell area; and (4) a poly Si TFT (thin film transistor) with an LDO (lightly doped offset) structure, all of which are based on a 0.4- mu m design rule using a SAC (self aligned contact) process. The access transistor with an N/sup -/ offset resistor increases the cell ratio without expanding cell size. The symmetrical cell configuration, the ground plate, and the TFT with the LDO structure contribute to cell operation stability.<<ETX>>

12 W/mm recessed-gate AlGaN/GaN heterojunction field-plate FET

A recessed-gate structure was introduced to improve transconductance (gm) and gain characteristics in AlGaN/GaN field-plate (FP) FETs. A maximum gm was improved from 130 to 200 mS/mm by introducing gate recess. Recessed FP-FETs exhibited 3-7 dB higher linear gain as compared with planar FP-FETs. A 1 mm-wide recessed FP-FET biased at a drain voltage of 66 V demonstrated 12.0 W output power, 21.2 dB linear gain, and 48.8 % power added efficiency at 2 GHz. To our knowledge, the power density of 12.0 W/mm is the highest ever achieved for GaN-based FETs.

Low-contact-resistance and smooth-surface Ti∕Al∕Nb∕Au ohmic electrode on AlGaN∕GaN heterostructure

We have achieved both low contact resistance and smooth surface morphology by using Ti∕Al∕Nb∕Au formed on an Al0.3Ga0.7N∕GaN heterostructure. A low contact resistance of less than 0.6Ω∕mm was reproducibly recorded after thermal treatment with a wide range of annealing temperature from 830 to 1000°C and annealing time from 10 to 300s. It was found that root-mean square surface roughness of under 35nm was obtained with all the annealing conditions investigated. In consideration of surface roughness and reproducibility, the most suitable annealing condition was 850°C for 100s, which leads to a contact resistance and a specific contact resistivity of 0.48Ω∕mm and 5×10−6Ω∕cm2, respectively.

Ka-band 2.3W power AlGaN/GaN heterojunction FET

Describes the first successful watt-level Ka-band power operation of an AlGaN/GaN heterojunction FET fabricated on a SiC substrate. Taking the advantage of high breakdown voltage, high-current, and high-gain characteristics of the short-channel GaN-based FET, state-of-the-art high-power performance of >2W has been achieved at 30GHz from a single chip having a gate width of 0.36mm. The developed device with a gate length of 0.25/spl mu/m exhibited a linear gain of 8.8dB at 30GHz, indicating that the short-channel AlGaN/GaN FET is promising for a variety of high-power applications at Ka-band and above.