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A power MESFET offering a high qadd operating at a very low VDD has been developed. MESFET has a buried p-layer and o u r improved LDD n+ self-aligned structure which include highly electrically activated ion-implanted regions due to rapid thermalcap annealing using double-layered SiN films deposited by ECR plasma CVD. The device geometries and implantation conditions were optimized s o as to achieve a high V(BR)cDo of more than 10 V and a low VI( of less than 0.5 V, and s o as to minimize the bias dependence of S-parameters. This produced excellent electrical characteristics such as Po INTRODUCTIONRecently, wirelesspersonal communication systems such as mobile telephones have required larger reductions in size, weight and power consumption. To do this, it is necessary that RF-power-amplifiers improve their power efficiency and lower their operating voltage. Moreover, in the case of applying them to digital telecommunication systems including such as a QPSK (Quadrature Phase Shift Keying) modulator, the amplifiers must have a low-distortion performance.We have developed GaAs power MESFETs with a high power-added efficiency qadd while operating at very low drain bias VDD for use in L-band medium-power amplifiers. In order to realize such device performance, its structure and ion-implantation conditions were optimized s o as to satisfy the following two requirements simultaneously. One is to achieve a high drain breakdown voltage V(BR)cDo of more than 10 V and to lower the drain knee voltage VK to less than 0.5 V in order to enlarge the voltage swing level of the output signal. This obtains a high drain efficiency

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An improved cluster matching circuit was proposed in which all of the gates and drains of FETs are connected with microstrip lines, respectively, and the gate and drain biases are applied without going through a divider or combiner. A method is also proposed for determining circuit constants to prevent even‐mode and odd‐mode oscillations. The present method proved effective when these techniques were applied to an L‐band power amplifier module. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 73–76, 1998.