L. La Spina

Bulk-Micromachined Test Structure for Fast and Reliable Determination of the Lateral Thermal Conductivity of Thin Films

A novel bulk-micromachined test structure is presented for the fast and reliable determination of the lateral thermal conductivity of thin films. The device is composed of a heater resistor and thermocouples that are fabricated in polysilicon (poly-Si), and the associated processing and DC measurement procedures are straightforward. The validity of the method is supported by numerical simulations and verified by experimental determination of the lateral thermal conductivity of aluminum (Al), aluminum nitride (AlN), p-doped poly-Si, and silicon nitride (SiN) thin films. For Al, an average value of 217 W m-1 K-1 was found for 1-mum thick layers. For the other layers, a number of thicknesses were studied, and the increase of thermal conductivity with thickness was effectively detected: for AlN, values from 7 to 11.5 W m-1 K-1 were found, and for p-doped poly-Si, values went from 21 to 46 W m-1 K-1 for thicknesses from 0.15 to 1 mum. For SiN, a value of 1.8 was extracted for layers thicker than 0.5 mum.

Improved RF Devices for Future Adaptive Wireless Systems Using Two-Sided Contacting and AlN Cooling

This paper reviews special RF/microwave silicon device implementations in a process that allows two-sided contacting of the devices: the back-wafer contacted silicon-on-glass (SOG) substrate-transfer technology (STT) developed at DIMES. In this technology, metal transmission lines can be placed on the low-loss glass substrate, while the resistive/capacitive parasitics of the silicon devices can be minimized by a direct two-sided contacting. Focus is placed here on the improved device performance that can be achieved. In particular, high-quality SOG varactors have been developed and an overview is given of a number of innovative highly-linear circuit configurations that have successfully made use of the special device properties. A high flexibility in device design is achieved by two-sided contacting because it eliminates the need for buried layers. This aspect has enabled the implementation of varactors with special Ndx -2 doping profiles and a straightforward integration of complementary bipolar devices. For the latter, the integration of AlN heatspreaders has been essential for achieving effective circuit cooling. Moreover, the use of Schottky collector contacts is highlighted also with respect to the potential benefits for the speed of SiGe heterojunction bipolar transistors (HBTs).

PVD Aluminium Nitride as Heat Spreader in SilicononGlass Technology

Physical-vapor-deposited aluminium nitride has been integrated in a silicon-on-glass NPN BJT process. Deposition conditions have been developed for which suitable electrical, mechanical and thermal properties are achieved. Electrothermal device characterization is used to demonstrate the effective heat spreading of this thin-film material

MEMS test structure for measuring thermal conductivity of thin films

A novel MEMS test structure and measurement procedure is presented with which the lateral thermal conductivity of thin films can be easily and accurately extracted. The extraction procedure is discussed in detail and supported by numerical simulations. Experimental examples are given for the determination of the lateral thermal conductivity of aluminium (Al), aluminium nitride (AlN), and p-doped polysilicon (polySi) thin films.

Evaluating the self-heating thermal resistance of bipolar transistors by DC measurements: A critical review and update

The most relevant techniques proposed in the literature for the extraction of the self-heating thermal resistance of bipolar transistors from measurements of their DC electrical characteristics are analyzed and compared for both GaAs HBTs and silicon BJTs. A simple procedure is presented to accurately evaluate the thermal resistance of silicon BJTs with non-negligible Early effect, for which traditional HBT-oriented methods are found to be of little value.

Electrothermal Effects in Bipolar Differential Pairs

The electrothermal behavior of bipolar differential pairs fabricated in silicon-on-glass technology is investigated. Experimental results demonstrate that a considerable distortion of the characteristics may occur when the individual transistors are sensitive to electrothermal effects, with consequent performance and reliability reduction. Simulations are employed to support the measurements and to examine methods to reduce the electrothermal feedback.

Special RF/microwave devices in Silicon-on-Glass Technology

This paper reviews special RF/microwave silicon device implementations in the back-wafer contacted Silicon-On-Glass (SOG) Substrate-Transfer Technology (STT) developed at DIMES. In this technology, metal transmission lines can be placed on the low-loss glass substrate, while the resistive/capacitive parasitics of the silicon devices can be minimized by a direct two-sided contacting. Focus is placed here on the device level aspects of the SOG process. In particular, complementary bipolar device integration and high-quality varactors for high-linearity adaptive circuits are treated in relationship to developments in back-wafer contacting and the integration of AlN heatspreaders.

Silicon-on-glass technology for RF and microwave device fabrication

This paper reviews the applications and potentials of back-wafer contacted silicon-on-glass (SOG) substrate-transfer technology (STT) particularly for RF and microwave silicon-device-design enhancement. This type of SOG process gives direct access to the part of the device that is usually connected via the bulk Si, by allowing advanced patterning and contacting of the backside of the wafer (back-wafer) with respect to the front of the wafer (front-wafer). In this manner the resistive and capacitive parasitics of the device itself, which in silicon often inhibit high-frequency (HF) performance, can be reduced to a minimum. At the same time new device concepts are made possible. Examples of fabricated devices (varactor diodes, vertical double-diffused MOSFETs (VDMOSFETs) and complementary bipolar transistors) are given and described in relationship to issues such as the very limited thermal budget permitted in the back-wafer processing and the inherently high thermal resistance of the SOG devices

FEAT - A Simulation Tool for Electrothermal Analysis of Multifinger Bipolar Transistors

In this paper, we present a new simulation tool, which can be effectively adopted for the electrothermal analysis of multifinger bipolar transistors. The program is based on an optimized procedure for solving the nonlinear system of equations governing the electrothermal device behavior. Features like model accuracy, short computation time, flexibility, and user friendliness make the proposed software a good candidate for optimizing both reliability and performance of modern transistors with complex layouts

Characterization of PVD aluminum nitride for heat spreading in RF IC's

Physical-vapor-deposited aluminum nitride, developed for heat spreading in RF ICs, is characterized by fabricating and measuring several different types of test structures. Among other things, it is shown that the material is a good dielectric insulator and has suitably low mechanical stress and piezoelectric response. With layers as thick as 6 mum, the electrothermal instabilities in a silicon-on-glass bipolar process are drastically reduced.