Substrate transfer for RF technologies

Abstract

Abstract-The constant pressure on performance improvement in RF processes is aimed at higher frequencies, less power consumption, and a higher integration level of high quality passives with digital active devices. Although excellent for the fabrication of active devices, it is the silicon substrate as a carrier that is blocking breakthroughs. Since all devices on a silicon wafer have a capacitive coupling to the resistive substrate, this results in a dissipation of RF energy, poor quality passives, cross-talk, and injection of thermal noise. We have developed a low-cost wafer-scale post-processing technology for transferring circuits, fabricated with standard IC processing, to an alternative substrate, e.g., glass. This technique comprises the gluing of a fully processed wafer, top down, to an alternative carrier followed by either partial or complete removal of the original silicon substrate. This effectively removes the drawbacks of silicon as a circuit carrier and enables the integration of high-quality passive components and eliminates cross-talk between circuit parts. A considerable development effort has brought this technology to a production-ready level of maturity. Batch-to-batch production equipment is now available and the technology and know-how are being licensed. In this paper, we present four examples to demonstrate the versatility of substrate transfer for RF applications.

Electrothermal Limitations on the Current Density of High-Frequency Bipolar Transistors

“…Here the thermal resistance becomes lower than the bulk silicon value. Such a technology is successfully implemented in experimental silicon-on-glass BJTs [12] and silicon-on-glass power MOSFETs [17]. Although the simulated structures are very simplified and three-dimensional effects are not included, the trend in self-heating is overly clear and illustrates the enormous significance of the device geometry 3.…”

“…Many substrate modification techniques are being introduced to improve transistor speed, improve the quality of integrated passives and reduce crosstalk. These include shallow and deep trench isolation, silicon-on-insulator (SOI) processes and substrate transfer [11], [12]. In all these methods, the electrically conductive silicon is replaced by electrical insulators that, unfortunately, also are very good thermal insulators and the thermal resistance of the devices can become forbiddingly high.…”

Extraction and modeling of self-heating and mutual thermal coupling impedance of bipolar transistors

“…Unfortunately, such solutions entail a tremendous reduction in the heat spreading from the active device regions [8]- [12]. Furthermore, emerging technologies based on three-dimensional (3-D) integration [13] and substrate transfer [14], [15], despite being electrically very attractive, continue degrading the heat spreading, influence self-heating and mutual thermal coupling, and increase the circuit operating temperature. It is, therefore, very important to accurately describe electrothermal feedback within a single device, and equally important to understand and describe electrothermal coupling within a circuit composed of such devices.…”

Single-grain Si thin-film transistors on flexible polyimide substrate fabricated from doctor-blade coated liquid-Si

“…Indium Gallium Zinc Oxide (IGZO), as a metal oxide semiconductor, shows higher electron carrier mobility than that of organic semiconductors, but it is impossible to make both PMOS and NMOS TFTs using the same metal oxide. 2 Transferring of CMOS-SOI chips 3 and amorphous Si (a-Si) transistors on plastics by laser release 4 have been reported. However, the former has cost and technical issues since the limited size of the wafer and pick and place process, and in the latter, the electrical performance is low, although the laser release technique requires less cost.…”