Tim Henderson

Physics of degradation in GaAs-based heterojunction bipolar transistors

Abstract The GaAs HBT has recently become the technology of choice in particularly demanding wireless communications applications. However, controversy about HBT reliability is still widespread, with conflicting claims for lifetime and activation energy. Here, we detail the fundamental physics of HBT degradation, and describe the stress factors that drive it. Extensive testing shows that degradation is typically due to the formation of midgap traps associated with crystalline defects in the base. In addition, we describe the physical reasons for the superiority of the GaInP emitter in reliable HBT design. Finally, we show preliminary results of a stress test on large area (2 × 45 μm 2 ) GaInP emitter HBTs which have lasted 5000 hours at 75 kA/cm 2 , 215 °C with no discernable degradation in device characteristics yet.

Efficient three-state WCDMA PA integrated with high-performance BiHEMT HBT / E-D pHEMT process

Power amplifiers for WCDMA applications must provide competitive power efficiency at low power levels as well as at full power. This paper presents a novel approach to obtain high PAE performance over a wide power band from three power states. It uses a novel BiHEMT process to co-integrate InGaP/GaAs HBT technology with InGaAs/AlGaAs E/D-Mode pHEMT into a single process. No bias reference voltage is required. Typical ultra-low power mode quiescent current is 5 mA.

Modeling gallium arsenide heterojunction bipolar transistor ledge variations for insight into device reliability

Abstract It is widely known that under normal bias conditions, GaAs heterojunction bipolar transistor (HBT) device degradation proceeds by a gradual buildup of defects in the base and base–emitter junction depletion regions. The buildup of these defects is associated with a solid-state phenomenon known as recombination enhanced defect reaction, which is the formation and migration of defects associated with nonradiative electron–hole recombination events. These defects are often associated with midgap traps, which serve as additional recombination centers for electron–hole pairs. The resulting increased recombination current is an additional base leakage current, which reduces current gain. By extension, a high electron–hole recombination density in a region with an initially high defect density––such as an unpassivated or poorly passivated base surface––will lead to quick device degradation. This paper reports the modeling of the effects of various different extrinsic base passivation ledge parameters––material composition, thickness, width, and spacing from ledge to base contact––to determine the microscopic effects these parameters have on electron–hole recombination density. Through this we can qualitatively predict the effects these parameters will have on HBT reliability.

High reliability high voltage HBTs operating up to 30 V

This paper reports the reliability characterization of InGaP/GaAs HBTs fabricated with a high voltage process. Breakdown voltages BV/sub ceo/ = 42 V and BV/sub cbo/ = 72 V are demonstrated, making this technology suitable for 28 V bias in most applications. Proprietary growth, unit cell design, and fabrication techniques ensure that current collapse is not seen at any bias point up to avalanche breakdown. Elevated temperature and current density bias stress tests at 16 V, 20 V, and 30 V show good reliability, with an extrapolated MTTF at nominal bias conditions and 140/spl deg/C junction temperature of at least 10/sup 7/ hours.

Study on mechanisms of InGaP/GaAs HBT safe operating area using TCAD simulation

The safe operating area (SOA) of InGaP/GaAs heterojunction bipolar transistors has been studied using two-dimensional Technology Computer-Aided Design (TCAD) tool. Comprehensive physical models, including hydrodynamic transport-based impact ionization and self-heating models were implemented. The simulations for two DC modes (constant I b and V b modes) captured all the SOA features observed in measurements and some failure mechanisms were revealed for the first time by TCAD simulations. The simulated results are also in agreement with analytical modeling. The simulation not only gives us insight to the detailed failure mechanisms, but also provides guidance for the design of devices with better ruggedness and improved SOA performances.

HBT lifetime prediction as a function of temperature

Make observations on HBT testing and how test conditions affect projected MTTF and Ea. Baseline bias stress data for TQS BiHEMT process active devices: HBT, D-mode pHEMT, E-mode pHEMT.