Richard J. Reay

Microfabricated electrochemical analysis system for heavy metal detection

A low power, hand-held system has been developed for the measurement of heavy metal ions in aqueous solutions. The system consists of an electrode array sensor, a high performance single chip potentiostat and a microcontroller circuit. The sensor is a microfabricated array of iridium electrodes, onto which a thin film of mercury is electroplated. Quantitative heavy metal analysis is performed using square-wave anodic stripping voltammetry. Measured results show a one part-per-billion sensitivity and multiple use capability.

An unconditionally stable two-stage CMOS amplifier

This paper describes a two-stage CMOS amplifier that is stable for any capacitive load. This is achieved through the use of an optimized cascoded compensation topology. A new level shifting technique allows independent optimization of drive capability, noise and systematic offset voltage. The circuit is 0.1 mm/sup 2/ in a 2 /spl mu/m technology and has a quiescent current consumption of 110 /spl mu/A. >

Micromachined thermally isolated circuits

Abstract This paper details a post-processing technique by which circuitry in an unmodified IC technology is thermally and electrically isolated from the silicon substrate. This method enables new applications for micromachining, including temperature regulation of analog ICs, to be carried out. The process is discussed in detail, along with improved tetramethyl ammonium hydroxide (TMAH) etching chemistries that use strong oxidizers to eliminate hillock formation. Also presented is an electrochemical biasing method that uses circuitry on the silicon being etched during the micromachining step. Work is currently underway to evaluate the use of these micromachining techniques for commercial analog circuit applications, several of which are discussed.

Thermally and electrically isolated single crystal silicon structures in CMOS technology

Thermally and electrically isolated single crystal silicon structures have been fabricated using a post-processing anisotropic tetramethyl ammonium hydroxide (TMAH) electrochemical etch. The process was carried out on CMOS circuits fabricated by a commercial foundry. Since the etch consists of a single micromachining step performed on packaged and bonded dice, this technique has the potential for cost-effective prototyping and production of integrated sensors and circuits.<<ETX>>

An integrated CMOS potentiostat for miniaturized electroanalytical instrumentation

Two major limiting factors in mass production and field use of electroanalytical instruments have been the size and cost of potentiostats. This monolithic CMOS potentiostat has performance comparable to bench-top instruments at a fraction of the size, power consumption and cost. A block diagram of the potentiostat chip is shown. An integrating DAC sets the voltage between the working electrode, where the electrochemical reactions of interest take place, and a chemically stable reference electrode. The control amplifier regulates this voltage using feedback to drive a third (counter) electrode. The working electrode current is measured with a current-input dual-slope ADC.<<ETX>>

Diode-based thermal r.m.s. converter with on-chip circuitry fabricated using CMOS technology

Abstract A high-frequency root-mean-square (r.m.s.) converter composed of two matched thermal elements and on-chip circuitry has been fabricated in a foundry CMOS process with post-process micromachining techniques. An anisotropic undercut etch in conjunction with an electrochemical etch stop is used to form the thermal elements of the r.m.s. converter, which are suspended single-crystal silicon regions containing temperature-sensing diodes heated by polysilicon resistors. One of the elements is heated by the a.c. signal, while an integrated continuous-time feedback network maintains a second element at the same temperature. The converter has a packaging-limited — 3 dB bandwidth of 415 MHz, an r.m.s. dynamic range of 53 dB, nonlinearity of 1%, a quiescent power dissipation under 1 mW, and occupies an area of approximately 400 μm × 400 μm. The thermoelements have a thermal resistance of up to 37 000 K W −1 in air. In addition to the r.m.s. converter itself, an improved wet etchant chemistry is presented. Ammonium persulfate, when added to tetramethyl ammonium hydroxide (TMAH) silicon etchant, improves the silicon etch rate and the (100) surface quality. This etch chemistry should be useful for a broad range of CMOS-compatible micromachining applications.

A micromachined low-power temperature-regulated bandgap voltage reference

This paper describes a temperature regulated bandgap voltage reference fabricated in a foundry CMOS process. Using a simple post-processing micromachining step, a small portion of the chip containing the reference circuitry is thermally isolated from the rest of the silicon die. Having high thermal resistance and small thermal mass, the reference requires 200 times less power and warms up 160 times faster than previous heated-substrate circuits. The reference, in a standard CMOS process, can be included on-chip with CMOS data converters and mixed-signal products.

Microfabricated Electrochemical Analysis System For Heavy Metal Detection

This paper describes a low power, hand-held heavy metal analysis system. The system consists of a microfabricated mercury drop electrode array, a high performance single chip potentiostat and a microcontroller circuit. Measured results show a one part-per-billion sensitivity and multiple use capability.

Electrically floating conductivity detection system for capillary electrophoresis

Abstract A conductivity detector is designed for capillary electrophoresis in which the detection electronics are isolated and float with the separation voltage applied to the capillary. This design minimizes the detrimental effect of the high voltage to the detection system and is powered using a battery. A simple arrangement is fabricated for the conductivity measurement electrodes. The electrical signal generated at these electrodes is carried through the floating electronics and then transmitted to a data-acquisition computer through a optical (infrared) serial link. As a preliminary demonstration, a sample solution containing three alkali metal ions is analyzed. The detection limits for the ions are about 2·10−6 M.

High-voltage Devices And Circuits Fabricated Using Foundry Cmos For Use With Electrostatic Mem Actuators

High-voltage n- and p-type MOS transistors were fabricated using the 2.0 /spl mu/m analog CMOS process available through the MOSIS foundry service. By using the n-well abd the p-base layers as lightly doped drains, breakdown voltages were 120V and -27V for the NMOS and PMOS structures, respectively. The corresponding Early voltages were -1000V for the NMOS and 240V for the PMOS devices. Amplifiers using the high-voltage devices were fabricated and used to drive all-aluminum electrostatic actuator structures. A first level SPICE model was also derived for the high-voltage transistors.