Low noise GaAs FET amplifier performance is enhanced at 1-2 GHz frequencies through the use of source inductance feedback. A simple circuit model predicts noise and signal performance and is used to derive matching circuits for the amplifier design. A 1-2 GHz single stage amplifier, designed on the basis of the modeled results, demonstrates <1.7dB noise figure, 15dB gain, and modest VSWR across the band. Over narrower bandwidths, <1dB noise figure with 15dB of associated gain and <3:1 VSWR is demonstrated.

falo Alto, CA PIN DIODES have been used for several years to accomplish switching in the VHF spectrum. Due to their relatively high minimum series resistance ( "0.5 ohm), they cannot be used in the UHF spectrum for band switching in applications requiring high circuit Q. A low resistance UHF (< 0.2 Q a t 20 mA, reverse bias capacitance, Cj G.8 pF) switching PIN diodc has been developed for this purpose, using techniques ba5ed on optimizing the diode performance and an improved device technology.An optimization technique was developed to minimize the resistance of the device from geometric considerations. The optimization program was devised by breaking the PIN diodc resistance into two parts: current-independent resistance and current-dependent resistance. The current-independent rcsistance (P' diffusion, N+ substrate, metal-semiconductor contacts) is PC Ppt PN+ pNt R =-+-where, A is the active area of the diode, pr is the contact resistivity, pp+ and pNt are the average resistivity of the P+ and Nt regions, respect&ely, and QP+ and . ! -? , t arc the lengths of the P 'and N+ regions, respectively.The current-dependent resistance can be written using the standard charge control model where, w is the width of the I layer, is the average elcctron and hole mobility, I is the diode current, and rcff is the effective minority carrier lifetime. Since Teff is a function of the I-layer width w and the current density J, this relation must he included.The exact relation is relatively complex, but the following empirical formula is a good approximation:where, 7 , is the effective lifetime at a given I-layer width, wo, and a given current density, J,. Using this relationship and the standard capacitance equationwhere, E is the dielectric constant, and C. is the junction capacitance, the currcnt-dependent part (I-layer resistance) can be written as J The mobility used is corrected due to carrier-carrier interactions at high current densities. Since the mobility is a slowly varying function of current density, it can be easily calculated by itcration. Typically two or three iteratious are adcquatc.The total resistance of the diode is thc sum of equations (I) and (5), There is obviously a minimum in the rcsistance as a function o f area, A. The area corresponding to minimum resistance is A . mm =&)6Using this area the I-layer width is determined from equation (4). This completely defines the active region of the diode.The total diode resistance can be reduced by decreasing K1 and K2. Several processing steps can be varied to decrease K1. rhin and heavily doped P+ diffusions are used to reduce the resistance of the Pf diffusion. By the use of Ti metal contacts and by keeping the surface concentration on both the Pf diffusion and theN+ substrate high (>lozo ~r n -~) :the metal contact resistivities are reduced.To reduce the N' substrate resistance, a process was developed to obtain a thin ( 3 p m ) substrate. The SEM photograph in Figure 1 shows the structure of the diode with the thin substrate.This device w a~ processed on (I ...

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The first gallium arsenide integrated circuit reported in 1974 contained a total of 5 depletion mode MESFETs which had a minimum 1 . 0~ gate length. The logicegates in this circuit had a minimum propagation delay of 75ps and consumed 9OmW of power, resulting in a 6.75pJ speed-power product. Chip size was 0.15 X 0.15mm. Circuit projections indicated that 2-3GHz clock rates would be feasible with logic circuits or binary dividers realized with such gates. I n 1977, a 0.4 X 0.44mm2 gate chip produced 4GHz toggle rates in a binary divider, and gate propagation delays of 142ps coupled with 2OmW/gate power resulted in speed power products of 2.8pJ i n depletion mode MESFET logic. Enhancement mode GaAs FET logic appeared at this time with 2 orders of magnitude reduction in speed-power product, achieving as low as 350ps X 0.074mW/gate = 26fJ per gate. At that time, comparable speed power products for silicon bipolar logic were loops X O.75mW/gate = 75fJjgate, or 85ps X 2.2mW/gate = 187fJ/gate. Frequency divider toggle rates were approximately '/z those possible with the gastest GaAs circuits.Thus, depending upon design choice, GaAs ICs could provide either the fastest operation, or the best power delay products, compared to silicon.These developments introduced an exciting new technology for high-speed digital integrated circuits, but it was recognized that the relative difficulty of fabricating gallium arsenide devices and circuits as compared t o standard silicon technologies, rendered gallium arsenide as a speciality product of research laboratories, of interest primarily in very high-speed applications which were not cost sensip tive. Indeed, the intervening several years have not found gallium arsenide used in major digital applications, even though microwave gallium arsenide discrete devices have become dominant in applications at high microwave frequencies.Gallium arsenide research reported recently is every bit as exciting as those first reports, but current work is beginning to demonstrate that the scale of gallium arsenide circuits is making it feasible for a great variety of high end applications. While the basic speeds have not changed significantly, the numbers of transistors in individual circuits has grown by orders of magnitude (to several thqusand), chip sires have grown in proportion (6mm2), and the introduction of a variety of devices and the variety of circuit techniques have made gallium arsenide integrated circuits far more sophisticated. Performance, for example in a 1Kb RAM, has attained 2.6ns memory access time at 291mW power dissipation (access time -power product = 757pJ) which is several times smaller than for similar silicon circuits. Coupled with the major cost reductions Seen in gallium arsenide products visible t o the industry, the promise of gallium arsenide integrated circuits products appears to be much closer t o reality.In this session, we will not only find a variety of circuits scaling from small scale integration up to large scale integration, but sophisticated process technology ...