Ronald Dekker

Substrate transfer for RF technologies

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.

An ultra low-power RF bipolar technology on glass

We present a new technology, SOA (Silicon-On-Anything) to transfer circuits processed on SOI substrates to another substrate, e.g. glass or alumina. We have used this technology to integrate an ultra low-power bipolar high-frequency process with high-quality passive components including spiral inductors. Circuits with record low-power RF performance are demonstrated.

A back-wafer contacted silicon-on-glass integrated bipolar process. Part I. The conflict electrical versus thermal isolation

A novel silicon-on-glass integrated bipolar technology is presented. The transfer to glass is performed by gluing and subsequent removal of the bulk silicon to a buried oxide layer. Low-ohmic collector contacts are processed on the back-wafer by implantation and dopant activation by excimer laser annealing. The improved electrical isolation with reduced collector-base capacitance, collector resistance and substrate capacitance, also provide an extremely good thermal isolation. The devices are electrothermally characterized in relationship to different heat-spreader designs by electrical measurement and nematic liquid crystal imaging. Accurate values of the temperature at thermal breakdown and thermal resistance are extracted from current-controlled Gummel plot measurements.

Optimizing RF front ends for low power

This paper discusses optimizations for the power dissipation of RF front ends in portable wireless devices. A breakthrough in power dissipation can be achieved by simultaneously optimizing the antenna interface, circuits, and IC technology of such devices. A model that predicts the minimum power dissipation of a front end for both short-range and long-range connections will be introduced. Using these models, the impact of the antenna interface on the power dissipation will be assessed. Using two antennas with equal gain combining, a typical power dissipation reduction of 2.5 to 30 times can be achieved. Using high-impedance circuits for short-range systems in combination with silicon-on-anything technology, a further reduction of power dissipation by up to one order of magnitude can be realized.

Longitudinal Poverty and Income Inequality a Comparative Panel Study for the Netherlands, Germany and the UK

A valve having a valve closing member rotatably supported on one or more valve stems which are positionally infinitely adjustable is disclosed. The valve has a valve body defining a bore with an upper passageway extending from the bore. A valve stem extends coaxially through the passageway and rotatably supports the valve closing member in the bore. A cartridge is coaxially located within the passageway between the valve body and the stem. The cartridge captures the valve stem and engages the passageway via screw threads allowing for infinite positional adjustment. The cartridge also houses bearings for rotation of the stem and seals for sealing the passageway. The valve body may have a second passageway coaxially aligned with the first passageway in which a second valve stem is located. The second stem engages the passageway via screw threads allowing for infinite positional adjustment. The adjustable stems allow the valve closing member to remain perfectly centered within the bore for maximum valve operational life.

Biocompatible encapsulation of CMOS based chemical sensors

One of the most challenging design aspects of chemical sensors is the isolation of the non-sensitive areas from the sensed medium. This becomes particularly critical in applications where the sensors are part of an implantable platform, restricting the available options to those using biocompatible materials. Parylene has been extensively used to coat pacemakers as it demonstrates excellent chemical, electrical and thermal stability. In this work, we have utilized parylene to encapsulate CMOS-based chemical sensors bonded on a cartridge, while the sensing area has been exposed by laser ablation and sonication. Measured results demonstrate improved electrical isolation than previously reported techniques.

Substrate transfer: enabling technology for RF applications

Substrate transfer is proposed as a wafer-scale postprocessing technology to transfer circuits processed with standard IC processing to an alternative substrate e.g. glass. The advantages of the complete elimination of RF coupling to the resistive silicon substrate are illustrated by several examples. The application of substrate transfer to III-V IC processes is proposed, and its extension to flexible ultra-thin circuits based on mono-crystalline silicon is demonstrated.

RF figures-of-merit for process optimization

Today, transistor y-parameters are routinely being measured for the determination of the current-gain cut-off frequency f/sub T/ and the maximum oscillation frequency f/sub max/. In this paper, it is shown that a much wider use of y-parameter measurements can be made for the RF characterization of transistors. A method is presented to determine the small-signal behavior of actual RF circuit-blocks from the measurements of the y-parameters of the individual circuit components. This is applied to define additional RF figures-of-merit for basic building blocks of analogue and digital RF circuits. No equivalent transistor circuit or compact-model parameters are needed, which is important for giving quick feedback to process developers. This approach is illustrated on three basic RF circuit blocks using bipolar transistors.

Silicon-Filled Rectangular Waveguides and Frequency Scanning Antennas for mm-Wave Integrated Systems

We present a technology for the manufacturing of silicon-filled integrated waveguides enabling the realization of low-loss high-performance millimeter-wave passive components and high gain array antennas, thus facilitating the realization of highly integrated millimeter-wave systems. The proposed technology employs deep reactive-ion-etching (DRIE) techniques with aluminum metallization steps to integrate rectangular waveguides with high geometrical accuracy and continuous metallic side walls. Measurement results of integrated rectangular waveguides are reported exhibiting losses of 0.15 dB/ λg at 105 GHz. Moreover, ultra-wideband coplanar to waveguide transitions with 0.6 dB insertion loss at 105 GHz and return loss better than 15 dB from 80 to 110 GHz are described and characterized. The design, integration and measured performance of a frequency scanning slotted-waveguide array antenna is reported, achieving a measured beam steering capability of 82 ° within a band of 23 GHz and a half-power beam-width (HPBW) of 8.5 ° at 96 GHz. Finally, to showcase the capability of this technology to facilitate low-cost mm-wave system level integration, a frequency modulated continuous wave (FMCW) transmit-receive IC for imaging radar applications is flip-chip mounted directly on the integrated array and experimentally characterized.

Residue-free plasma etching of polyimide coatings for small pitch vias with improved step coverage

The authors have found that patterning polyimide coatings containing organosilane adhesion promoter using pure oxygen plasma resulted in a thin silicon-rich residue layer. They show in this paper that adding small amounts of fluorine-containing gas to the etching gas mixture is necessary in order to achieve residue-free polyimide plasma etching. They report residue-free plasma etching of polyimide coatings with both isotropic and anisotropic profiles, using either metal or oxide hard masks. These etching methods are however not sufficient for the fabrication of high density metal filled vias in 10 μm thick polyimide coatings. In order to improve the metal step coverage over the vias while keeping the pitch as small as possible, the authors have developed a two-step etching recipe combining both isotropic and anisotropic profiles, resulting in wine-glass shaped vias.