W. Alan Davis

Thermal modeling of the non-linear thermal resistance of the SiGe HBT using the HICUM model

The existing industry standard compact models, VBIC and HICUM, are used to model devices using a linear thermal resistance network. However, the thermal resistance of the SiGe Heterojunction Bipolar Transistor (HBT) depends on the amount of power dissipated in the device. The increase of thermal resistance caused by self-heating due to the unsymmetrical emitter geometry and deep trenches lead to a non-linear relation between temperature and power dissipation. In this paper, a current controlled voltage source (CCVS) is used to account for the variation in current to model the thermal resistance of the device.

A loop-breaking method for simulation of feedback circuits using a VCVS-terminated subnetwork model

A model for a multi-terminal subnetwork is applied in a loop-breaking method for open and closed-loop analysis of feedback circuits. The model contains two physically disconnected subnetworks having specific terminals connected to grounded voltage-controlled voltage sources (VCVS). Gain pa-rameters of the VCVSs control signal transfer through the model allowing a feedback loop to be opened or closed in a switch-like manner. The method is applied in circuit analysis and simulation where closed-loop dc bias conditions are imposed on the open-loop circuit. Small-signal analysis of the equivalent circuit produces Bodes return-ratio and return difference corresponding to the modeled component.

Thermal characterization of the VBIC dielectrically isolated device

This paper presents thermal characterization of the dielectrically isolated bipolar junction transistor (DIBJT) with the vertical bipolar inter-company (VBIC) model. The VBIC model incorporates the thermal nodes of a transistor. Semiconductor devices are strongly influenced by the thermal effects. When the device is heated, it raises its local temperature which changes the devices intrinsic parameters. This paper shows the behavior of collector current, base current, thermal transconductances, and junction temperature versus temperature. It also shows several other temperature characteristics of a VBIC DIBJT device.

Fabrication processes of MEMS phase shifters on polymer-based substrates

RF phase shifters find wide applications in telecommunications, satellite systems, personal wireless communication systems, radar systems, tracking systems, and sensors. They have been conventionally manufactured by semiconductor technologies which suffer from high insertion losses due to high RF series resistances. They are expensive due to fabrication and assembly costs. The RF MEMS phase shifters provide low insertion losses, low fabrication costs and high linearity compared with the semiconductor ones. Furthermore, polymer materials have demonstrated low material costs and low RF attenuations. In this work, we proposed to build RF MEMS phase shifters on polymer substrates. The proposed devices were successfully manufactured and tested from DC to 26 GHz. Our experimental results indicated more than 35 degrees phase shifts and low insertion losses.

GaAs RF Wafer Qualification using RF Probes

Processing of Gallium Arsenide MMICs is expensive due in part to the time required to RF-qualify wafers. Manufacturers who intend to compete in this relatively new market must reduce device costs. To reduce a MMICs cost a major emphasis should be on early detection and discontinuation of wafers which will not yield devices meeting the MMICs expected RF performance. On-wafer RF qualification can be established as a technique to achieve this goal.