David W. Palmer

UWB communication using SAW correlators

A simple approach to ultra-wideband (UWB) communication has been demonstrated using surface acoustic wave (SAW) correlators to provide direct RF-to-baseband conversion. The SAW correlators used are bi-phase shift key (BPSK) coded devices that can directly generate or detect an RF signal. This continuous wave (CW) approach to UWB communication is markedly different from the prevailing pulse-based techniques and offers advantages of simplicity, lower component count, and lower cost. The resulting transmitter and receiver architectures eliminate mixers, IF amplifiers, IF filters, and most baseband signal processing. Transmitters and receivers were built operating at 915 MHz, 2.43 GHz, and 5.6 GHz using SAW correlators with 1.25%, 3.3%, 12.5% ,25%, and 50% fractional bandwidths.

Extreme Temperature Range Microelectronics

Down-hole geothermal instrumentation must operate over a large temperature range. The technology and capabilities of room temperature to 300°C hybrid and printed-circuit (PC) board electronics that were developed during the last two years to meet that need are summarized. To ensure rapid widespread commercialization, this technology was developed, insofar as possible, using commericaUy available components, devices, and materials. Initial extensive high-temperature characterization revealed that selected thickfilm passive components and silicon junction-field-effect transistors had electrical parameters sufficiently insensitive to temperature change and sufficiently constant in time at high temperatures to form the backbone of this circuitry. Attachment techniques needed to be developed, since standard methods failed at high temperatures. Similarly, circuit design innovations were needed because of the restricted list of parts. Voltage regulators, line drivers, voltage comparators, special purpose amplifiers and multiplexers were constructed and operated over the 25-300°C temperature range. Temperature and pressure monitoring instruments using these circuits have been used for downhole measurements in geothermal wells. Methods of fabrication, circuit performance, and the scope of future work are discussed.

Short and long loop manufacturing feedback using a multisensor assembly test chip

A family of silicon test chips for use in making diagnostic measurements during electronics assembly has been developed. These assembly test chips (ATCs) contain sensors that measure a number of variables associated with assembled IC degradation, including the degree of integrated circuit (IC) corrosion, handling damage, electrostatic discharge threat, moisture or humidity, mechanical stress, mobile ion density, bond pad cratering, and high-speed logic degradation. The chips in the ATC family are intended to give manufacturing feedback in four ways: direct feedback in evaluation of an assembly manufacturing line in an objective, nonintrusive way; before and after comparisons on an assembly production line when an individual process, material, or piece of equipment has been changed; resident lifetime monitor for system package aging and ongoing reliability projection; and thermal, mechanical, DC electrical, and high-frequency mock-up evaluation of packaging (including multichip) schemes. >

Mode locking in arrays of superconducting weak links

Abstract The independent Josephson oscillation of individual elements in a series array of proximity coupled bridges becomes spontaneously synchronized into a single mode when the interbridge spacing is made sufficiently small.

High frequency SAW correlator module

Surface Acoustic Wave (SAW) correlators were developed which function with central kequencies ranging fiom 300 h4Hz to 2.7 GHz. These devices enable direct translation of data to RF and back without the use of intermediate frequency stages. Several impediments to the manufacture of SAW correlators were overcome. In addition, a programmable SAW correlator built as a flip-chip combination of lithium niobate on silicon was demonstrated.

Aluminum Wire to Thick-Film Connections for High-Temperature Operation

Hybrid microcircuits in geothermal instrumentation must operate from room temperature to 300°C. Bond failure occurred during operation of initial geothermal circuits due to intermetallic growth at the aluminum wire-to-gold conductor interface. To remedy this problem, two wire bonding techniques have been qualified in high-temperature aging tests: 1) ultrasonic bonding of aluminum wire directly to modified fritless gold conductor inks (DuPont 9910, AVX 3520, and TFS A328) and 2) insertion of a I mil diffusion barrier pad between the thick film and the aluminum wire. Both systems allow 100-1000 h operation at 300°C. Three alloys of wire were tested: pure aluminum, aluminum with I percent silicon, and aluminum with 1 percent magnesium. The degradation rates differed greatly with pure aluminum being the least tolerant to temperature aging and wire with 1 percent silicon faring best. Because thick-film surfaces tend to be harder than thin-film surfaces, hardened aluminum wire (elongation 0.5 percent) formed bonds with less pad deformation and, consequently, with higher pull strengths than standard bonding wire (elongation 1-3 percent). Comparison of wire bonds aged at three temperatures (250, 300, and 350°C) demonstrated several orders of magnitude spread in degradation rates; for 1000-h bond lifetime, 300°C was found to be about the highest allowed operational temperature for direct bonding to gold. Disks of kovar and nickel of l-mil thickness and 30 mils diam were used as diffusion barriers between the gold and aluminum. Evaporated on one side of each disk was a 1 µm gold thin film for thermocompression bonding to the thick film; the other side received an evaporated aluminum film for wire bonding. Aging for 1000 h up to 350°C produced no increase in bond resistance for any of the three wire alloys tested. Some decrease in pull strength with time was noticed but was attributed to annealing of the wire.

IC chip stress during plastic package molding

Approximately 95% of the worlds integrated chips are packaged using a hot, high pressure transfer molding process. The stress created by the flow of silica powder loaded epoxy can displace the fine bonding wires and can even distort the metallization patterns under the protective chip passivation layer. In this study we developed a technique to measure the mechanical stress over the surface of an integrated circuit during the molding process. A CMOS test chip with 25 diffused resistor stress sensors was applied to a commercial lead frame. Both compression and shear stresses were measured at all 25 locations on the surface of the chip every 50 milliseconds during molding. These measurements have a fine time and stress resolution which should allow comparison with computer simulation of the molding process, thus allowing optimization of both the manufacturing process and mold geometry.

Real-time RF spectrum analyzer: Components and system development

Many wireless communication links quickly hop between narrow frequency channels. Many such connections can occur simultaneously in the same band and hop in a standard pseudorandom frequency pattern dwelling a predetermined time in each channel. To sense modern communication, a real-time spectrum analyzer is very useful. One large advantage of real time analysis is that it only records data in active channels because it can determine the activity in each time interval. Another advantage is that communication that is not adhering to FCC standards can also be discerned. A van full of RF amplifiers, digitizers, and Fourier analysis equipment has been used for this job in non-real time. We chose to attack this design by providing many identical signal paths, one for each frequency channel. A number of RF components had to be developed to make this circuit power efficient and fit a small footprint. The initial broad band signal from an antenna sees low noise amplification (LNA) and then is divided into many identical RF signal paths using silicon germanium integrated circuits (SiGe RFICs). Each of these RF signals is filtered by one filter in a ladder of frequency adjacent SAW filters. The output of each SAW device is compared with the RF power seen in the previous time interval to see if there is less or more of a signal. Up to this point the system has been low- power analog. Once the RF channel powers are quantified, the system uses a digital signal processor (DSP) to further analyze signal characteristics.

Re-configurable Completely Unpowered Wireless Sensors

A methodology for remotely and wirelessly reading any type of unpowered impedance varying sensor is described. Unpowered wireless sensors, in existence for a number of years, have been limited to low impedance sensors. Techniques for reading high impedance sensors are introduced here. The resulting methodology can be used to measure a wide range of different sensors, including temperature, pressure, light level, mechanical switch, acoustic emission, and acceleration. These sensors report physically measurable data in the same manner as do similar conventional sensors, but they do it remotely and without any local power source. The sensors are measured remotely using a radar-like interrogation device, and the sensors and their related communication electronics draw all of the power needed for communicating from the radar pulse.

Microsystem packaging of an RF SAW correlator

An electrically programmable surface acoustic wave (SAW) correlator was recently completed from design through small scale production in support of low power space-based communications for NASA. Three different versions of this RF microsystem were built to satisfy design requirements and overcome packaging and system reliability related issues. Flip-chip packaging and conventional thick film hybrid assembly techniques are compared in the fabrication of this microsystem.