James B. Angell

An Integrated-Circuit Approach to Extracellular Microelectrodes

This paper describes a new multielectrode microprobe which utilizes integrated-circuit fabrication techniques to overcome many of the problems associated with conventional microelectrodes. The probe structure consists of an array of gold electrodes which are supported on a silicon carrier and which project beyond the carrier for a distance of about 50 ? to allow a close approach to active neurons. These electrodes are covered with a thin (0.4-?) layer of silicon dioxide which is selectively removed at the electrode tips using high-resolution photoengraving techniques to define the recording areas precisely. The processing sequence described permits any two-dimensional electrode array to be realized. Interelectrode spacings can be accurately controlled in the range from 10 to 20 ? or larger, and electrode-tip diameters can be as small as 2 ?.

A Low-Capacitance Multielectrode Probe for Use in Extracellular Neurophysiology

A multielectrode structure containing integrated junction-FET input stages is described. Photoengraved microelectrodes are utilized to obtain high dimensional precision, small size, and extremely low capacitive coupling between electrodes. The interelectrode capacitance is less than 0.01 pf. The integrated input devices (JFETs) reduce the impedance levels on the recording channels to less than 500 ohms, virtually eliminating crosstalk and stray noise pickup from the system. The n-channel JFETs operate as source-followers from a common 2.5 volt drain supply and have input impedances greater than 100 megohms at 1 kHz. A simple external preamplifier ensures stable operation and easy interfacing with conventional recording and display equipment. Special considerations in the design of low-noise completely integrated input stages for use with metal microelectrodes are discussed in detail. As a result of the low interelectrode coupling in this structure, simultaneous recording and stimulation from closely adjacent areas of brain should be possible with virtually no stimulus artifact.

An IC Piezoresistive Pressure Sensor for Biomedical Instrumentation

A thin-diaphragm piezoresistive pressure sensor for biomedical instrumentation has been developed using monolithic integratedcircuit (IC) techniques. The piezoresistive effect has been chosen for this device because it provides an observable resistance change that is a linear function of pressure and is observable at low stress levels. A diaphragm is used as a stress magnifying device; its magnification is proportional to the square of the ratio of the diaphragm diameter to its thickness. The pressure-induced stresses in the diaphragm are sensed by properly oriented piezoresistors interconnected to form a bridge.

A microprobe with integrated amplifiers for neurophysiology

A multielectrode probe containing integrated buffer amplifiers, capable of recording the activity of single neurons in the brain, has been fabricated using IC technology, The probe overcomes the stray coupling-noise limitations of conventional microelectrode recording systems.

A microminiature fluidic amplifier

Abstract A microminiature fluidic amplifier with vertical-walled features 6 μm wide and 35 μm deep has been fabricated in silicon using dry anisotropic etch

An IC piezoresistive pressure sensor for biomedical instrumentation

A thin-diaphragm diffused piezoresistive pressure sensor has been developed for biomedical instrumentation using monolithic IC techniques. Anisotropic etching affords large-area, 5μ thick diaphragms with high yield, and simple temperature compensation eliminates residual temperature drift.

Microprocessors get integrated sensors: Sensing devices and signal processing built into one silicon chip portend a new class of ‘smart’ sensors

Considers the development of silicon microsensors which can fit on the same chip with a microprocessor. Various sensor types are described, their fabrication presented and their possible applications pointed to.