This work is the creation of Large Area Restructurable Silicon System (LARSS) which involve arrays of both integrated circuits and transducers. This work aims at the creation of new silicon systems that can readily be expanded to areas and complexities much larger than current integrated circuit fabrication limits. To increase circuit area to the wafer scale level, 10-200 times the current IC area, requires defect avoidance technologies bypass IC fabrication errors and hook together working sections to create large systems. The technique divides the system into redundant circuit blocks surrounded by a grid of metal signal/clock/power bus lines to which the devices can be connected. In all cases the designs use standard IC fabrication services (eg. Canadian Microelectronics Corp.) to manufacture the devices, but applies post fabrication processing to achieve the unique systems. One interconnecting technique which makes permanent signal routing uses a laser linking system developed by the applicant at M.I.T. Lincoln Laboratory and currently applied at Simon Fraser University. It consists of two separated dopant lines in the silicon substrate which are connected to the bus lines (like a gateless transistor). An external laser melts the gap area causing the dopant lines to connect with a resistance of typically 60 ohms. The laser can also cut metal lines, thus segmenting the signal buses.

Wafer Scale Integrated 16 point FFT  From M.I.T Lincoln Lab Laser linking by G. Chapman,  design by M. Rhodes

In terms of work here my students and I have built a major unique piece of experimental equipment. This is a laser interconnection table which will focus a controlled laser beam on integrated circuits with a 0.1 micron position repeatability. This is one of only five such systems in the world, two at M.I.T. Lincoln Lab, plus one each at the University of South Florida and the US National Security Agency. I have played a major part in the creation of all such systems, and feel this is the best designed so far. The value of this equipment is demonstrated by the interest in using the laser table shown in the Industrial Cooperation section.

Due to the expensive nature of building true wafer scale systems my work has concentrated on studying techniques for building large area systems and the design of new classes wafer scale type devices. At the VLSI design level this has resulted in building circuits to compare the area and speed tradeoffs for defect avoidance of laser connections and active devices, which has lead to the design of circuits combining both for optimum operation. My research has proposed and tested a new type of large area product: the Wafer Scale Field Programmable Gate Array which could increase the density of current FPGA systems by 10-100 times. Another new concept was LARSS systems containing both transducers (some micromachined), control circuitry and the laser redundancy network needed to build in large areas. First proposed in one of my papers, the idea here is to build large transducer arrays using separate types of redundancy layouts for both the transducers and the circuitry. One such systems is a large area magnetic field sensor array designed for mapping magnetic field distributions being undertaken by my PhD student Yves Audet. Another array was a design for a wafer scale array of thermal emission elements. In this transducer matrixes the laser redundancy scheme changes the design from something that can be used only in small chip sized structures (say 10x10 arrays) to very large devices possibly of 256 x 256, which makes it of considerable interest to several organizations.
Click here for papers on WSI projects
Currently this wafer scale work has concentrated on the development of large area optical sensors.  (see Lasers/Optical/Sensor Applications)

Laser/Optical/Sensor Applications

Laser micromachining is used to create unique devices not possible with current etching technology. The most import work here is a vision/proximity sensor called "Vision Skin" developed by myself and my grad students for the Canadian Space Agency. Vision Skin gives both gives a low resolution image of the an approaching object and measures the distance to it with precision 100 micron precision. This patented device has been licensed by the Canadian Space Agency and Kinetic Sciences Inc. Click here for papers on the Vision Skin  project   This is part of the Angular Domain Imaging work (see the Biomedical Sensor section)

In addtion to the laser links a Laser Microsurgery on Integrated Circuits service for Canadian Microelectronic Corp. members has been offered using my laser table during the past four years. Removing defects occurring in chip designs has been done for researchers directed to this laboratory by CMC. Specifications for this service is maintained by CMC on their web site. The most important and successful project consisted of a nearly 8 months project with McGill's Electronic department. A very large IC, consisting of about 40% of the area of a CMC 1.2 micron fabrication run, contained several design defects which made them totally inoperable. The size of the chip meant that it would be very expensive to refabricate. In a series of experiments involving the exchange of 5 sets of chips the problems were identified by successive cut and test cycles. The final work produced fully operable devices, enabling the student to obtain his thesis. Several local companies have used this laser microsurgery to analyze problems with their chips and reduce the design cycle.

Micromachining

Laser Micromachined Biomedical Sensors

A unique UV laser micromachining facility has been funded by Canadian Foundation for Innovation grant and is currently being built up in our lab. This will be used to build biomedical devices cooperative research with two companies. These consist of precisely shapped plastics holding patterns of electrodes which make contact to the nerves. We build these by an ultraviolet (UV) laser on a computer controlled micropositioning table to create 3D structures with photoablation: where the UV photon's energy literally tears apart the molecules of plastics and allows the automated shaping of materials. The computer controlled UV laser table system will allow cuff design and electrode positions to be altered from one test sample to another, for rapid design evolution.

Microfabrication

Bimetallic thermal alloying resists consist of two thin metal films. In and Bi, in this case, are RF or DC sputtered to the thickness of 15-150 nm on a thin film layer that is going to be patterned. When exposed to light under a photomask, as shown in, the material in the exposed area will absorb the light energy and be heated up to above the Bi/In eutectic temperature. Since the alloy has a lower melting point than either individual film, melting will begin at the interface between the two layers and move outward as the melt pool grows.  At the end of the laser pulse, the resist layers will cool and solidify as the eutectic alloy. The material in the unexposed area, where the light is blocked by the photomask, will remain the same as two-layer structure. Tests show that the alloy have different chemical properties from Bi or In.  For the resist development after exposures, two etch solutions have been found which will attack the areas of unexposed resist more aggressively than the exposed areas. After the resist development, the alloyed area remains while the unexposed area is removed. The pattern is then transferred to the underneath layer to be patterned by plasma etching or wet etching. After the resist stripping, the whole lithography process is completed.This project is supported by a grant from CREO Products, the BC Advanced Systems Institute and BC Science Council.
Click here for papers on the Inorganic Resist project

Space Applications

The potential advantage of Microfabrication in space has been under study by my research team at Simon Fraser University.  The project was first conceived in 1990 during my period on the research staff of Massachusetts Institute of Technology’s Lincoln Laboratory microelectronic group where I was principal researcher on the Restructurable Wafer Scale Integration project.  The project proceeded at a modest level, with a first publication in 1991 while the questions were considered.  Starting in 1998 Boeing Aircraft funded a more intense research phase was entered which culminated in a Masters project by Nick Pfeiffer.  This carefully investigated the main technical problems, issues, costs and benefits of space.  Studies showed that successful space microfabrication needed to change the existing wet organic photoresist process for a vacuum based dry resist process.  Several such process to do this have been proposed in the literature.
Click here for papers on space microfabrication
Howver, one of the considerable synergies of our work is the development under a separate program of a Inorganic Dry thermal resist for CREO Products, a world leader in applications of organic thermal resists.  (see Microfabrication section)

Another space related project is the Vision Skin proximity and imaging sensor work is continuing in a cooperative program with the Canadian Space Agency. See the Laser/Optical Sensors area.

Computer/Internet Anti-theft technology

Links To Other Descriptions of My Research