Timothy D. Strong

Solid-state ion sensors with a liquid junction-free polymer membrane-based reference electrode for blood analysis

Abstract A set of ion-selective membranes for the measurement of clinically relevant electrolytes, i.e., K+, Na+, Ca2+, H+ and Cl−, and a solvent-processible polyurethane (PU)-based reference membrane were cast on metal electrodes patterned on small ceramic plates, and on silicon-based sensors. Since the liquid junction-free PU membrane-based reference electrode provides a constant potentiometric signal for an extended period of time, accurate determination of blood electrolytes could be made without using a separate reference flow. The PU membrane-based reference electrodes not only improve the mass producibility of miniaturized solid-state ion sensors but also simplify the configuration of flow cell cartridges without compromising their analytical performance.

A low-voltage, chemical sensor interface for systems-on-chip: the fully-differential potentiostat

Amperometric chemical sensing systems implemented in deep-submicron processes can meet the dimensional and functional requirements for bio-implantable and remote sensing applications. The low-voltage nature of these processes, however, limits the functionality of the sensors electronic interface, the potentiostat. A new, fully-differential (FD) potentiostat that mitigates these problems is presented. The FD potentiostat was implemented in TSMCs 0.18 /spl mu/m CMOS process and experimentally verified. The circuit maintains full functionality while operating at half the supply voltage of standard architectures. Analytes of biological and environmental importance are chemically analyzed using the FD potentiostat. Results indicate that the FD potentiostat enables system-on-chip sensor technology which may one day lead to pervasive sensing.

A Fully Differential Potentiostat

Low-voltage, single-ended (SE) potentiostats are unable to detect many analytes of interest because the oxidation potentials of these analytes are greater than the voltage that the potentiostat can deliver to the electrodes. In this work, a fully-differential (FD) potentiostat is described which enables detection of a wide range of analytes using a supply voltage of 1.8 V. The FD potentiostat was implemented in TSMCs 0.18 mum CMOS process and has been verified experimentally. A theoretical discussion of the FD potentiostat is given and comparisons to SE potentiostats are provided. Biological and environmental analytes are chemically detected using the FD potentiostat.

Ion sensors using one-component room temperature vulcanized silicone rubber matrices

Abstract Two different types of one-component room temperature vulcanized (RTV) silicone rubbers (Dow Corning 3140 and 730 RTV) are further examined as alternatives to PVC for formulating ion-selective membranes. The four different ionophores used in this work are: valinomycin (K+), ETH 1001 (Ca2+), tridodecylamine (H+) and trifluoroacetyl-p-decylbenzene (CO32−). Ion-selective RTV membranes are made by incorporating an ionophore along with a plasticizer and/or an ionic additive (i.e. either plasticized or non-plasticized). In most cases, potentiometric ion responses and selectivities of RTV-based membranes, when formulated properly, compare favorably to those of corresponding PVC-based membranes. In general, 730 RTV is found to be better suited for formulating plasticizer-free membranes. The preferred matrices are a plasticized 3140 RTV for Ca2+ and a non-plasticized 730 RTV for CO32−. Planar solid-state sensors fabricated with selected RTV membrane formulations are shown to function well with a stable response signal and an extended sensor lifetime.

A microelectrode array for real-time neurochemical and neuroelectrical recording in vitro

The development of a silicon neural recording device capable of measuring neurochemical and neuroelectrical activity in tissue culture is described. It consists of a microfabricated array of platinum and chloridized silver electrodes on a silicon substrate. A culture chamber affixed to the surface of the device contains the culture medium and cells. Neuron cultures were viable for over 75 days in the devices, generating both neuroelectrical and neurochemical data in real-time. The resolution and speed of the device allows for the study of single neuron interactions with the ability to correlate electrical signals directly with chemical responses.

Design, Implementation, and Verification of a CMOS-Integrated Chemical Sensor System

Single-chip chemical microinstruments offer many benefits over bench-top laboratory equipment. This work presents the design, implementation, and verification of a CMOS-integrated microinstrument including voltammetric sensors and electronic interface on a single silicon substrate. Both component and system design parameters are detailed. Mixed-domain models of the system which can be simulated in a standard CAD environment are generated and used for system optimization. The integrated device was implemented by post-processing sensor structures on top of AMIS-fabricated, 0.5 µm CMOS electronics. Fabrication details are discussed and experimental device characteristics including functionality and lifetime testing are presented. The completed device has an active area of 0.6mm² with sensors sites measuring 64 µm². It operates from a 3V supply and consumes 1.6mW

Integrated electrochemical neurosensors

Arrays of silicon neurosensors have been fabricated in our group for detection of both electrical signals and neurotransmitter levels in human neuron cultures. Neurochemical sensing of dopamine and its metabolites is provided by voltammetry. Passive neurochemical arrays have been tested in living human neuron cultures throughout a study period of seventy-five days. Calibration curves for dopamine taken in culture media with equipment optimized for the sensors suggests detection limits for dopamine below 100nM. To improve response, prototype devices incorporating active circuitry were developed. These active devices were formed by post-processing standard CMOS die fabricated through the MOSIS service, to form the sensor-specific features. We also describe a fully-differential potentiostat which has been developed for implantable biological applications and briefly describe future directions for our work

Area I/O flip-chip packaging to minimize interconnect length

This paper discusses an approach using area interconnect to achieve high performance for an experimental multichip microprocessor. The described method is being used in the PUMA project at the University of Michigan to design a processor that has a clock speed goal of 1 GHz. The approach relies on the coordinated placement of functional blocks on chips, and the resulting chips on the MCM. The use of area array pads to provide high bandwidth interconnections between the chips, and low inductance power connection to the MCM is also essential. Three stages of MCM development for the project are described.

Integrated microtransducers and microelectronics for environmental monitoring

Current research on a microsystem for the remote analysis of rainwater is presented. This project combines work in low-power microelectronics, microfabrication, electroanalytical chemistry, and environmental science to produce a system that analyzes the temporal and spatial dispersion of pollution. These analyses can lead to verification of environmental models and improved environmental health. The system incorporates voltammetric and potentiometric electroanalytical sensors, and microelectronic instrumentation. The entire system can be fabricated on a single substrate using standard CMOS processing for the instrumentation and post-CMOS processing of the sensors. Results from a two-chip model of the system match theory and demonstrate that the system is a viable solution for the remote monitoring of precipitation.

2.12 – Chemical Sensors

In recent years, chemical sensing microsystems have become the de facto standard for many day-to-day tests performed both in the laboratory settings and in the field. A few examples of how these types of microsystems are used today are the monitoring of biological fluids for illicit drugs in the workplace, point-of-care clinical testing, and the monitoring of toxic substance levels in industrial effluents. This chapter describes the principles of action and fabrication techniques for electrochemical sensors designed to monitor liquid-phase chemicals. The chapter begins with an introduction to electrochemical theory that describes the fundamental electrochemical equations, the methods of electrochemical transduction, and the principal components of an electrochemical cell. The chapter next describes two electrochemical transduction techniques, potentiometry and voltammetry. Descriptions of the most common measurement methods for sensors based on these two techniques and sample fabrication flows for each type of sensor as well as a comparison of the two techniques are presented. The remainder of the chapter describes the integration of chemical sensors and electronics, and packaging considerations for liquid-phase chemical sensors.