Tatsuya Hashinaga

Radiation tolerant GaAs MESFET with a highly-doped thin active layer grown by OMVPE

A novel GaAs MESFET structure with high radiation tolerance is proposed. Changes in electrical parameters of a GaAs MESFET as a function of total gamma -ray dose were found to be caused mainly by a decrease in the effective carrier concentration in an active layer. The structure was designed from a simulation based on an empirical relationship between the changes of the effective carrier concentration and the total gamma -ray dose. It was successfully demonstrated by utilizing a highly doped thin active layer (4*10/sup 18/ cm/sup -3/, 100 AA) grown by organometallic vapor-phase epitaxy (OMVPE). This MESFET can withstand a dose ten times higher (1*10/sup 9/ rads(GaAs)) than a conventional one can. >

Effect of CVD-SiO/sub 2/ film on reliability of GaAs MESFET with Ti/Pt/Au gate metal

The effect of CVD-SiO/sub 2/ films on the reliability of GaAs MESFET with Ti/Pt/Au gate metal was investigated. It was found that the mean time to failure (MTTF) of MESFET with 350/spl deg/C-depositied SiO/sub 2/ was only about one-seventh of that of the ones with 440/spl deg/C-SiO/sub 2/. It was also found that, in the storage test at 300/spl deg/C for 24 hours, diffusion of Pt into GaAs was accelerated when the SiO/sub 2/ deposition temperature was lower than 380/spl deg/C. FT-IR spectra indicated that the lower deposition temperature leads to a higher concentration of the residual hydrogen in SiO/sub 2/. Thermal differential spectrometry (TDS) demonstrated that hydrogen in SiO/sub 2/ could migrate even below 300/spl deg/C. In conclusion, the residual hydrogen in SiO/sub 2/ causes the degradation phenomena.

Pre-distortion linearizer module using InGaP-HBT based MMIC for LDMOS high-power amplifier

We have developed a miniature and simple pre-distortion linearizer module for Wide-band code division multiple access (W-CDMA) base station power amplifier. Si-LDMOS FETs are widely used as final stage for this application. In general, the same Si-LDMOS device has also been used as pre-distorter to cancel distortion made at the final stage. However, the circuits become complex and larger in size. We took a different approach by using InGaP HBT based MMIC (monolithic-microwave integrated circuit) as pre-distorter and achieved a simple, compact pre-distorter with ease of use. By using this pre-distortion linearizer module, we have demonstrated 15 dB reduction of adjacent channel leakage power ratio (ACLR) on 800 MHz band power amplifier (PA) and over 6 dB reduction on 2.1 GHz band PA. ACLR<-55 dBc@42 dBm was achieved and ACLR was improved for a broad power range in both PAs.

A High Power and Low Distortion AlGaAs Hetero MESFET with a Graded Pulse-doped Channel for Base Station Applications

This paper reports on high power GaAs MESFET for base station applications, which has been improved over conventional GaAs MESFET in several aspects. High uniformity and high yield are achieved with a planar structure by using an n+ implantation and rapid thermal anneal (RTA) process rather than a recess process. Breakdown voltage and gate leak current are improved by the insertion of an AlGaAs-cap layer for usage in high drain voltage operations more than 10V. A graded pulse-doped channel is an active layer in which doping concentration increases exponentially toward the buffer layer, prevents output power deviation for bias drain current The AlGaAs hetero MESFET shows high gain (18dB), high output power (450mW/mm), and low intermodulation distortion (IP3=40dBm) at 1.9GH, which demonstrates excellent performance for digital wireless base station applications.