Masami Nagaoka

Characterization of reactively sputtered WNx film as a gate metal for self‐alignment GaAs metal–semiconductor field effect transistors

Properties of reactively sputtered WNx films on a GaAs substrate have been investigated by electrical and physical analyses. WNx films were deposited from a pure W target by using three types of sputtering systems: (1) Magnetron sputtering system equipped with rf and dc mode; (2) S‐gun sputtering system; (3) rf diode sputtering system. The composition of WNx films was easily and reproducibly controlled by changing the N2 content in Ar–N2 mixed ambient gas. The WNx–GaAs system was both electrically and metallurgically stable even after high‐temperature annealing of up to 800 °C. The Schottky barrier height to n‐type GaAs was more than 0.8 V, which is the highest value obtained so far among any other refractory metals. Self‐aligned GaAs MESFET’s were successfully fabricated using a WNx gate. The transconductance was typically 150 mS/mm for 1.5 μm gate length.

A novel resonant-type GaAs SPDT switch IC with low distortion characteristics for 1.9 GHz personal handy-phone system

A GaAs SPDT switch IC operating at a low power supply voltage of 2.7 V has been developed for use in Personal Handy-Phone System in the 1.9 GHz band. In combination with MESFETs with low on-resistance and high breakdown voltage, the resonant-type switch IC utilizes stacked FETs and an additional shunt capacitor at the receiver side in order to realize low insertion loss, high isolation and low distortion characteristics. An insertion loss of 0.55 dB and an isolation of 35.8 dB were obtained at 1.9 GHz. The IC also achieved a second order distortion of -54.3 dBc and an adjacent channel leakage power of -66 dBc at 600 kHz apart from 1.9 GHz at 19 dBm output power.

Refractory WNx/W Self-Aligned Gate GaAs Power Metal-Semiconductor Field-Effect Transistor for 1.9-GHz Digital Mobile Communication System Operating with a Single Low-Voltage Supply

We have developed a refractory WNx /W self-aligned gate GaAs power metal-semiconductor field-effect transistor (MESFET) for use in L-band digital mobile communication systems. This power MESFET operates with high efficiency and low distortion at a gate bias of 0 V and a low drain bias of 2.7 V, because of its small drain knee voltage, high transconductance and sufficient breakdown voltage. This power MESFET is quite promising for a highly efficient linear power amplifier IC operating with a single low-voltage supply. Good output characteristics of the power MESFET with 1 mm gate width were attained for π/4-shifted quadrature phase shift keying (QPSK) modulated input signals in the 1.9-GHz band, such as an output power of 18.4 dBm, a power gain of 19.0 dB and a high power-added efficiency of 26.4% when a sufficiently low adjacent channel leakage power of -58 dBc was obtained.

A self-aligned gate GaAs MESFET with p-pocket layers for high-efficiency linear power amplifiers

This paper describes a newly developed GaAs metal semiconductor field-effect transistor (MESFET)-termed p-pocket MESFET-for use as a linear power amplifier in personal handy-phone systems. Conventional buried p-layer technology, the primary technology for microwave GaAs power MESFETs, has a drawback of low power efficiency for linear power applications. The low power efficiency of the buried p-layer MESFET is ascribed to the I-V kink which is caused by holes collected in the buried p-layer under the channel. In order to overcome this problem, we have developed the self-aligned gate p-pocket MESFET which incorporates p-layers not under the channel but under the source and drain regions. This new MESFET exhibited high transconductance and uniform threshold voltage. The problematic I-V kink was successfully removed and an improved power efficiency of 48% was achieved under bias conditions, which resulted in adjacent channel leakage power at 600-kHz offset as low as -59 dBc for 1.9-GHz /spl pi//4-shift QPSK modulated input.

High-efficiency monolithic GaAs power MESFET amplifier operating with a single low voltage supply for 1.9-GHz digital mobile communication applications

A monolithic GaAs power amplifier IC using refractory WN/sub xW self-aligned gate power MESFETs has been developed for 1.9-GHz digital mobile communication systems, such as the Japanese personal handy phone system. The power amplifier operates with high efficiency and low distortion with a single low voltage supply of 2.7-3.0 V, by virtue of small drain knee voltage, high transconductance and sufficient breakdown voltage of the power MESFET. An output power of 23.7 dBm and a high power-added efficiency of 24.2% were attained at 3 V for 1.9-GHz /spl pi4-shifted QPSK (quadrature phase shift keying) modulated input when adjacent channel leakage power was -58 dBc at 600 kHz apart.<<ETX>>

High efficiency, low adjacent channel leakage 2-V operation GaAs power MESFET amplifier for 1.9-GHz digital cordless phone system

A low-voltage GaAs power amplifier for 1.9-GHz digital mobile communication applications such as PHS handsets has been developed, using refractory WNx/W self-aligned gate MESFETs with p-pocket layers. This power amplifier operates with a single low 2-V supply, and an output power of 21.0 dBm, a power gain of 22.3 dB, a low dissipated current of 162.9 mA and a high power-added efficiency of 38.5% were attained with a low 600-kHz adjacent channel leakage power of -58.0 dBc for 1.9-GHz /spl pi//4-shifted QPSK modulated input.

A 2-V operation RF front-end GaAs MMIC for PHS hand-set

A single 2-V operation RF front-end MMIC has been developed using three kinds of self-aligned gate MESFETs. Its transmitter block of a power amplifier with an antenna switch exhibited a power gain of 28.9 dB and a high power-added efficiency of 27.0% at 20.5-dBm output power. The receiver block of a low-noise amplifier with the antenna switch exhibits a noise figure of 3.4 dB and a gain of 11.1 dB.A single 2-V operation RF front-end MMIC has been developed using three kinds of self-aligned gate MESFETs. Its transmitter block of a power amplifier with an antenna switch exhibited a power gain of 28.9 dB and a high power-added efficiency of 27.0% at 20.5-dBm output power. The receiver block of a low-noise amplifier with the antenna switch exhibits a noise figure of 3.4 dB and a gain of 11.1 dB.

A symmetric GaAs MESFET structure with a lightly doped deep drain for linear amplifiers operating with a single low-voltage supply

An improved symmetric GaAs MESFET structure with a lightly doped deep source/drain is proposed for application to power amplifiers in mobile communication terminals. With lightly doped deep drain, the impact ionization falls as the electron current expands and the current density decreases. Thus, the breakdown voltage rises, while a high transconductance and low parasitic resistance are maintained. Furthermore, the symmetric structure suits for mass production because of its fabrication process without mask alignment precision. This structure was fabricated using the WNx/W self-aligned gate process, and DC and RF characteristics were evaluated. The power-added efficiency was 37% at an adjacent channel leakage power of -55 dBc for 37%-shift QPSK modulated input signals at 1.9 GHz with a single positive supply voltage of 3 V. The efficiency was also high at a lower supply voltage: 34% at 1.2 V.

Single low voltage supply operation GaAs power MESFET amplifier with low-distortion gain-variable attenuator for 1.9-GHz personal handy phone systems

A GaAs power amplifier with a low-distortion, 10-dB gain attenuator has been developed for 1.9-GHz personal handy phone system (PHS). Single low 2.4-V supply operation was achieved by using power MESFETs with p-pocket layers. Furthermore, on account of an attenuator with cascaded shunt FET structure, very low 600-kHz adjacent channel leakage power (ACP) with sufficient, constant output power was attained regardless of any controlled gain. An output power of 21.1 dBm, a low dissipated current of 157 mA and a high power-added efficiency of 37.2% were obtained with ACP of -55 dBc.

A novel cap-annealing technique using a WN/sub x/ film as a capsulant in the refractory gate self-aligned GaAs MESFET fabrication process

A novel cap-annealing technique for n/sup +/ implanted layers in GaAs MESFETs was investigated from the viewpoint of thermal stress relaxation. In this technique, the same metal as the gates-tungsten nitride (WN/sub x/) was used for an underlayer of a double-layer annealing cap. FET parameters V/sub th/, K-value, and N/sub g/ showed behavior in the short-channel region just as if the short-channel effects were suppressed. >