A. Platzker

An AlGaAs/InGaAs pseudomorphic high electron mobility transistor with improved breakdown voltage for X- and Ku-band power applications

The authors determined that RF drain current degradation is responsible for the poor power performance of wide-recessed pseudomorphic high-electron-mobility transistors (PHEMTs). A model based on surface states was proposed to explain this phenomenon, which then led to the use of charge-screen layers and a double-recessed gate process to suppress surface effects. Combined, these two modifications increased the devices gate-drain reverse breakdown voltage without causing a degradation in the transistors RF drain current. This allowed the simultaneous achievement of high power-added efficiency and high power density which established a new performance record for power PHEMTs at X- and Ku-bands. Delay time analysis of single- and double-recessed PHEMTs revealed that the benefit of a larger breakdown voltage in the latter device design came at the cost of a larger drain delay time. Drain delay accounted for 45% of the total delay when the 0.35- mu m double-recessed PHEMT was biased at V/sub ds/=6 V. >

Characterization of GaAs devices by a versatile pulsed I-V measurement system

The authors build and utilized a pulsed I-V system which is capable of reaching any current-voltage point of three-terminal devices from any arbitrarily chosen DC bias point. The system, which can be used on wafer, serves as an invaluable tool for device modeling and process diagnostics. Direct dependence of the pulsed I-V curves on the DC bias was found in GaAs MESFETs and HEMTs (high-electron mobility transistors).<<ETX>>

Instabilities diagnosis and the role of K in microwave circuits

Many papers and textbooks and the leading CAD (computer-aided design) packages state that a two-port is stable if and only if K>1 and mod Delta /sup s/ mod <1 (or an equivalent set of conditions). The authors point out that the stipulation that the statement is rigorous only if no poles of the unloaded circuit lie in the right half plane is sometimes overlooked by current microwave designers who rely on K and mod Delta /sup s/ mod for determining the stability of their designs. Two examples are presented to illustrate the limited role of K in determining the stability of microwave circuits. The first example is an amplifier which was designed and manufactured in MMIC (monolithic microwave integrated circuit) form and the other is a simple study model of a ring oscillator. Both circuits fulfill all the above conditions for all omega but nevertheless exhibit strong microwave oscillations.<<ETX>>

A novel MMIC biphase modulator with variable gain using enhancement-mode FETS suitable for 3 V wireless applications

A circuit topology for realizing a BPSK (180 degree) modulator without the use of reactive phase determining networks is presented for the first time. This physically small circuit employs a trio of enhancement mode MESFETs which are uniquely configured to extend the upper frequency response of the design to in excess of 1.7 GHz. This approach is particularly noteworthy as it is implemented using less than 3 V dc and precludes the need for negative gate voltages making it attractive for use in wireless applications.<<ETX>>

2 and 4 watt Ka-band GaAs PHEMT power amplifier MMICs

The design and performance of power amplifiers for Ka-band applications is presented. A three-stage amplifier demonstrated 22 dB small signal gain from 26.5 GHz to 31.5 GHz and saturated output power of 4W with 28% power added efficiency from 28 GHz to 31 GHz. Record power density of 670 mW per mm of device output periphery was achieved. The amplifiers were fabricated on a selective double-recess 0.2 /spl mu/m GaAs power pHEMT process.

A double-recessed Al/sub 0.24/GaAs/In/sub 0.16/GaAs pseudomorphic HEMT for Ka- and Q-band power applications

A double-recessed 0.2- mu m-gate-length pseudomorphic HEMT (PHEMT) has been demonstrated with 500 mW of output power (833 mW/mm of gate periphery), 6-dB gain, and 35% power-added efficiency (PAE) at 32 GHz. At 44 GHz, the device exhibited 494 mW of output power (823 mW/mm), 4.3-dB gain, and 30% PAE. This level of performance is attributed to excellent MBE material, optimized epitaxial layer design, and the use of individual source vias and of double recess with tight channel dimensions. Excellent 3-in-wafer uniformity was also observed: DC yield was greater than 95% and the interquartile range for all DC parameters was less than 20% of the median value (most are significantly lower).<<ETX>>

One watt, very high efficiency 10 and 18 GHz pseudomorphic HEMTs fabricated by dry first recess etching

The authors report 10- and 18-GHz power performance of double recessed 1.2-mm periphery pseudomorphic high electron mobility transistors (PsHEMTs). They have obtained demonstrably better uniformity in performance than conventionally fabricated PsHEMTs. This was accomplished by incorporating a new approach to recess formation using selective reactive ion etching of the first recess in a double recessed structure. The critical first recess was formed with exceptional uniformity using dry etching and an AlGaAs etch stop layer. Simultaneous power, gain, and power-added efficiency, representative of many devices, are summarized.<<ETX>>

A novel 4-18 GHz monolithic matrix distributed amplifier

The authors describe the design, fabrication, and performance of a 4-18 GHz matrix distributed amplifier which incorporates a novel biasing scheme enabling the amplifier to run at higher voltages while drawing only half of the current of conventional multistage amplifiers having comparable gain levels. A voltage divider is used at the input of the FET pair to derive the gate bias, ensuring that both FETs are biased at the same point. This scheme enables the stages to be connected in cascade at RF frequencies and in cascode for DC biasing, thus conserving current. The amplifier shows >13 dB gain across the frequency band using a chip area of only 1.9 mm*2.1 mm.<<ETX>>The authors describe the design, fabrication, and performance of a 4-18-GHz matrix distributed amplifier. This amplifier incorporates a novel biasing scheme which enables the stages to be connected in cascade at RF frequencies and in cascode for DC biasing, thus conserving current. A gain of 14 dB+or-1.5 dB has been measured over the 4-18-GHz frequency band in a chip area of only 1.9 mm*2.1 mm.<<ETX>>

An AlGaAs/InGaAs pseudomorphic high electron mobility transistor (PHEMT) for X- and Ku-band power applications

A PHEMT with record-high output power, gain and power-added efficiency at 10 and 18 GHz has been achieved due to the use of a novel method to improve the gate-drain reverse breakdown voltage. A critical surface problem was uncovered and resolved. Silicon nitride was deposited as surface passivation. The results of this work suggest that, in addition to superior low-noise performance, the PHEMT is also very promising for high-performance, power amplications in the X- to Ku-band frequency range.<<ETX>>

Distributed small signal model for multi-fingered GaAs PHEMT/MESFET devices

A fully distributed equivalent circuit PHEMT and MESFET model is presented in closed form expressions for single finger end-fed FET geometry. The model includes self and mutual inductances and a new frequency dependent gate resistance. The model was used successfully to model multi-fingered devices which were subjected to equi-phase gate and drain excitations. Comparisons between measured data and model results are shown to be in excellent agreement for all S-parameters to 50 GHz regardless of unit gate width. Scaling issues are also investigated for the new distributed model.