We report on 1.9-GHz performance of the Buried-Channel self-aligned WN/W-gate GaAs MESFET (BC-MESFET) for use in digital mobile telephone handsets with low power consumption. The BC-MESFET incorporates undoped i-GaAs epitaxial-grown surface layer on the ion-implanted channel. Both the power and noise performance of the BC-MESFET are superior to the conventional MESFET. The 0.6-µm gate power BC-MESFET exhibits a high power-added efficiency of 57% at 1-dB gain compression, which leads to low power dissipation of the handset. This power performance is attributed to high breakdown voltage which the undoped i-GaAs surface layer has brought about. The BC-MESFET has also shown a minimum noise figure of below 0.4 dB. Taking the IC-oriented fabrication process of the BC-MESFET into consideration, these FET performances demonstrate that the BC-MESFET is suitable for the single-chip MMIC that integrates RF front-end blocks for the 1.9-GHz small-size mobile telephone handset with long battery lifetime.

A 15-50 GHz-band GaAs MMIC variable attenuator has been developed for microwave and millimeter-wave wireless communications systems. The attenuator employs a balanced distributed configuration using shunt connected HEMT's in order to realize a broadband operation, a low insertion loss and a good impedance matching with simple control bias scheme. The MMIC was fabricated with a pseudomorphic HEMT device technology. It has exhibited an insertion loss as low as 1.6 dB with an attenuation control range as wide as 21 dB at 26 GHz. It has also shown a good linearity of an input power of more than 12 dBm at 1-dB compression point and that of 26.3 dBm at a 3rd-order intercept point.

We have developed a GaAs direct-conversion π/4 shifted QPSK modulator IC equipped with variable attenuators for controlling the output power level of the 1.9 GHz Personal Handy Phone system in Japan (PHS). The IC was successfully demonstrated showing state-of-the-art performance with the image rejection ratio of more than 36 dBc at a low input power of -10 dBm in 1.9 GHz frequency range. By using the "Gate Current Control method by Pull-down FET's" (GCCPF), the equipped attenuators vary the output power from 0 dB to -28 dB by 4 dB step. The IC operates at a 2.7 V supply with power dissipation of 259 mW. The 2.64.6 mm2 chip with about 400 elements was fabricated by a 0.5 µm WNx-gate BPLDD GaAs MESFET process.

In this paper, we describe the effect of p-regions on the I-V kink in GaAs FETs. A kink-free p-pocket-type self-aligned gate GaAs MESFET (PP-MESFET), which does not include p-regions under the channel, has been analyzed and compared with a conventional buried-p-type self-aligned gate GaAs MESFET (BP-MESFET) using two-dimensional device simulation. The relation between the I-V kink and the layout of p-regions has been demonstrated by numerical simulation for the first time. For both the BP-MESFET and PP-MESFET, impact ionization produces holes in high-field regions. The holes accumulate under the channel, widen the channel, and cause an abrupt increase in drain current in turn in the BP-MESFET. On the other hand, in the PP-MESFET, holes generated in the high-field region are transported to the source region easily over the lower barrier owing to the absence of p-regions under the channel. Holes do not accumulate under the channel, leading to kink-free I-V characteristics of the PP-MESFET. P-regions should be located so as not to cause the accumulation of holes in GaAs FETs where p-regions are required for high-frequency performance.