AuGe/Ni ohmic contacts are used as source and drain electrodes of pseudomorphic HEMTs (pHEMTs). High alloying temperatures are generally believed to be necessary to enhance penetration of the alloy materials through the AlGaAs layers in order to establish a very low resistance path for the source-drain currents to access the two-dimensional electron gas (2DEG) layer. Here we have performed alloying experiments in the temperature range of 390-450 • C, and the contact resistance was determined using transfer length method measurements. Germanium diffusion was studied using backside secondary ion mass spectrometry. During our study, we have observed that doping of the channel by germanium is possible even at lower temperatures. But alloying at lower temperatures does not appreciably enhance the concentration throughout the different device layers below the contact pads. Hence, unlike MESFET alloying, higher alloying temperatures are essential for increasing the doping concentration so as to reduce the contact resistance and overcome the resistance of the AlGaAs layers.

This paper presents design, mathematical analysis, and measurement of low noise singlestage transimpedance amplifier (TIA) with scalable bandwidth using 130 nm bipolar complementary metaloxide-semiconductor (BiCMOS) silicon-germanium (SiGe) process. Common-emitter (CE) shunt-shunt feedback topology with active inductor peaking has been used in the design for improving noise, gain and driving capability of TIA by decreasing the input and output impedance, respectively. The use of active inductive peaking in CE shunt-shunt feedback topology has resulted in a new TIA configuration with better performance. The circuit has been optimized for low noise performance by adopting the proposed design technique. Validity of the mathematical analysis and design for the proposed TIA has been established with the help of simulations as well as measurement results. The measurement results of Ku-band TIA (10 MHz to 14 GHz) have demonstrated a transimpedance gain of 53.2 dBΩ, input-referred current noise of 16.8 pA/ √Hz with power consumption of 9.8 mW . The design architecture is adaptable for higher frequency bands, which has been demonstrated by designing another TIA covering K-and Ka-bands (10 MHz to 35 GHz) with transimpedance gain of 33.4 dBΩ, input-referred current noise of 29.4 pA/ √Hz with power consumption of 28.1 mW in the post-layout simulation results, and occupies same chip area as that of 14 GHz, i.e., 0.1 × 0.21 mm 2 INDEX TERMS BiCMOS, CE topology, inductive peaking, low noise, silicon-photonics, TIA

This paper presents a new attenuator bit topology selection algorithm for attenuator design to simultaneously achieve low amplitude and phase error with minimum insertion loss. The significance of this algorithm has been demonstrated by the design and implementation of 8-bit digital attenuator using 65 nm Complementary Metal-Oxide-Semiconductor (CMOS) technology in 2.8 GHz to 4.0 GHz frequency band. To meet the 8-bit attenuation and phase error resolution, new phase compensated Pi-, T-and T-bridge attenuator bit topologies are proposed in place of conventional attenuator bits from 32 dB to 0.25 dB. Performance of this attenuator has been validated with the help of exhaustive post layout parasitic simulation results. The integrated attenuator has demonstrated the highest ever reported attenuation precision at lowest root mean square (RMS) phase error and RMS amplitude error, i.e., 8-bit performance with maximum insertion loss of 5.1 dB, maxmum RMS phase error of 0.78°and maximum RMS amplitude error of 0.1 dB, input referred 1 dB compression point (IP 1 dB )>+14.8 dBm, input and output matching <−12 dB, in 2.8 GHz to 4.0 GHz with 1.55 mm × 0.35 mm chip area. This significant improvement in the attenuation precision, RMS amplitude and phase error of the integrated attenuator is the result of, systematic design approach, selection of each attenuator bit architecture using the proposed attenuator bit selection algorithm and incorporation of phase compensation techniques.