John Kevin Twynam

Bump heat sink technology - A novel assembly technology suitable for power HBTs

A novel assembly technique, bump heat sink (BHS), suitable for compound semiconductor power HBTs is proposed and demonstrated. In this technique, the heat generated in the transistor junction is effectively conducted away through a gold bump which is located on the top of each transistor unit. Using this technique, power transistors are demonstrated with power added efficiencies /spl eta//sub add/ of 74%, 66% and 61% for 5.0 W, 8.0 W and 10.0 W output CW, respectively, at 0.9 GHz with V/sub cc/=6 V. A three-stage HBT MMIC power amplifier for GSM class 4 is also demonstrated with /spl eta//sub add/ >55% at V/sub cc/=4 V CW operation.<<ETX>>

Thermal stabilization of AlGaAsGaAs power HBTs using n-AlxGa1−xAs emitter ballast resistors with high thermal coefficient of resistance

Abstract The use of n -Al x Ga 1− x As an emitter ballast layer material for AlGaAs GaAs heterojunction bipolar transistors (HBTs) is proposed and demonstrated. A high thermal coefficient of resistance can be obtained owing to the temperature dependence of the relative populations of the conduction band Γ, L and X valleys if the Al mole fraction x of the n -Al x Ga 1 − x As ballast layer is adjusted to give the appropriate intervalley energy separation. Al 0.3 Ga 0.7 As and Al 0.35 Ga 0.65 As emitter ballast layers incorporated in HBT structures have an average thermal coefficient of resistance of about 8 × 10 −3 °C −1 , which is significantly higher than that of GaAs ballast resistances. The temperature stabilizing effect of n -Al x Ga 1− x As ballast layer is assessed by measuring the d.c. current-voltage characteristics of single-emitter finger and multi-emitter finger HBTs. Large power HBTs with integrated n -Al x Ga 1− x As ballast resistors have been fabricated and an output power of up to 10 W at 0.9 GHz has been obtained.

Analytical model for electrical and thermal transients of self-heating semiconductor devices

Transients of self-heating semiconductor devices are theoretically investigated based on a feedback circuit model, which is composed of three sub-circuits describing the isothermal electrical characteristics, thermal impedance, and temperature dependence of the electrical characteristics of the devices, respectively. Analytical expressions of the frequency and transient responses have been derived for both the electrical and thermal characteristics of self-heating devices, yielding accurate methods to extract the thermal time constant in both the time and frequency domains. The model is verified by the transient electrical-response measurement of a GaInP/GaAs heterojunction bipolar transistor.

Demonstration of a 77-GHz heterojunction bipolar transferred electron device

We demonstrate for the first time a heterojunction bipolar transferred electron device (HBTED), a device with a bipolar transistor-like structure in which Gunn oscillations occur. The use of a graded doping profile in the collector region is, we believe, a key factor in the device design. AlGaAs/GaAs HBTEDs fabricated on semi-insulating GaAs substrates exhibit free-running oscillations at a frequency of around 77 GHz. The third (emitter) terminal enables this device to be injection-locked and to function as a self-oscillating mixer.

Optimization of the HBT and bump configuration for bump heat sink structure and application to HBT power MMICs

Abstract Suitable HBT and bump configuration for the BHS (Bump Heat Sink) structure are experimentally investigated. The best results in terms of thermal and electrical characteristics is obtained from the combination of a single emitter finger and an “H” shaped bump. Power HBTs are demonstrated with typical power added efficiencies ηadd of 70% at 8.0 W and a linear power vs transistor size relation up to 10 W at 0.9 GHz CW with Vcc = 6 V, using the optimized structure. A three-stage HBT MMIC power amplifier and a power amplifier module for GSM class 4 are demonstrated with ηadd of 53% at 5.0 W, for Vcc = 6 V CW operation, also using the optimized structure.

Design and analysis of heterojunction bipolar transferred electron devices

The design of the heterojunction bipolar transferred electron device (HBTED) is considered. MOCVD-grown AlGaAs/GaAs HBTEDs were fabricated and 60 GHz operation was confirmed by on-wafer measurements. Analysis of the device operation is aided by the use of Monte Carlo device simulations, equivalent circuit model simulations and two-dimensional (2-D) drift-diffusion model simulations and the simulation results are compared with measurements on the fabricated HBTEDs and HBTED test structures. The effects of the external base-collector region and current spreading in the collector region are investigated and the latter is found to be of great importance. Our simulations show that having an appropriately graded collector doping profile can compensate the current spreading and this hypothesis is supported by measurement results. Conclusions are drawn regarding the design of practical HBTEDs for mm-wave oscillator applications.

Simulation of Self-heating HBTs Based on Isothermal Gummel-Poon Model

Based on the correlation between the electron and hole injection currents at the emitter junction, a simple dc model of self-heating HBTs has been developed by introducing three physically-based parameters into the isothermal Gummel-Poon model, which is easy to construct and implant to circuit simulators. Both the self-heating and the anbient temperature effects can be simulated accurately. The electrical and thermal parameters of HBTs can be evaluated from the extracted model parameters, and a novel method for separating the base current components has also be developed.