Christopher W. Storment

Silicon fusion bonding and deep reactive ion etching: a new technology for microstructures

Abstract New developments in deep reactive ion etching (DRIE) technology, when combined with silicon fusion bonding (SFB), make it possible, for the first time, to span nearly the entire range of microstructure thicknesses between surface and bulk micromachining, using only single-crystal silicon. The combination of these two powerful micromachining tools forms a versatile new technology for the fabrication of micromechanical devices. The two techniques are described and a process technology is presented. Some of the experimental structures and devices that have been demonstrated using this new process technology are discussed.

Regeneration microelectrode array for peripheral nerve recording and stimulation

A microelectrode array capable of recording from and stimulating peripheral nerves at prolonged intervals after surgical implantation has been demonstrated. The microelectrode array, fabricated on a silicon substrate perforated by multiple holes (referred to as via holes), is implanted between the ends of a surgically severed nerve. Regenerating tissue fixes the device in place to provide a stable mapping between the microelectrodes and the axons in the nerve. Processes were developed for the fabrication of thin-film iridium microelectrodes, micromachined via holes, and silicon nitride passivation layers. All fabrication methods were designed to be compatible with standard CMOS/BiCMOS processes to allow for on-chip signal processing circuits in future designs. Such arrays, implanted in the peroneal nerves of rats, were used to record from and stimulate the nerves at up to 13 months postoperatively.<<ETX>>

Silicon-substrate microelectrode arrays for parallel recording of neural activity in peripheral and cranial nerves

A new process for the fabrication of regeneration microelectrode arrays for peripheral and cranial nerve applications is presented. This type of array is implanted between the severed ends of nerves, the axons of which regenerate through via holes in the silicon and are thereafter held fixed with respect to the microelectrodes. The process described is designed for compatibility with industry-standard CMOS or BiCMOS processes (it does not involve high-temperature process steps nor heavily-doped etch-stop layers), and provides a thin membrane for the via holes, surrounded by a thick silicon supporting rim. Many basic questions remain regarding the optimum via hole and microelectrode geometries in terms of both biological and electrical performance of the implants, and therefore passive versions were fabricated as tools for addressing these issues in on-going work. Versions of the devices were implanted in the rat peroneal nerve and in the frog auditory nerve. In both cases, regeneration was verified histologically and it was observed that the regenerated nerves had reorganized into microfascicles containing both myelinated and unmyelinated axons and corresponding to the grid pattern of the via holes. These microelectrode arrays were shown to allow the recording of action potential signals in both the peripheral and cranial nerve settings, from several microelectrodes in parallel.<<ETX>>

Plasma-etched neural probes

Abstract A new method is presented for microfabricating silicon-based neural probes that are designed for neurobiology research. Such probes provide unique capabilities to record high-resolution signals simultaneously from multiple, precisely defined locations within neural tissue. The fabrication process utilizes a plasma etch to define the probe outline, resulting in sharp tips and compatibility with standard CMOS processes. A low-noise amplifier array has been fabricated through the MOSIS service to complete a system that has been used in multiple successful physiological experiments.

Microfabricated heavy metal ion sensor

Abstract A novel microfabricated electrochemical sensor has been developed for the detection and measurement of heavy metal ions in aqueous media. The sensor consists of a silicon substrate, on which is fabricated an electrically interconnected, but diffusionally isolated, array of thin-film iridium microelectrodes upon which a thin film of mercury is electrodeposited. Square-wave anodic-stripping voltammetry is used for quantitative analysis. This method involves an initial preconcentration phase in which the array is held at a cathodic potential such that the metal ions are reduced and amalgamated into the mercury, followed by anodic stripping (re-oxidation) of the metal ions. The charge required to strip a given ionic species completely is proportional to its initial concentration in the test solution. Sensitivity in the parts per billion range has been demonstrated without the addition of supporting electrolytes, deoxygenation, agitation, or any other alterations to the water samples.

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.

Organic thermal and electrostatic ciliary microactuator array for object manipulation

Abstract An organic thin-film ciliary microactuator array using independent thermal and electrostatic actuation is described. A polyimide thermal bimorph structure provides for large angle deflection with high load capacity. Electrostatic electrodes provide low-power hold-down, capacitive sensing, and feedback control capabilities. Integrating four orthogonally oriented actuators into a unit cell and replicating this cell into an array allows for precise movement of small objects in arbitrary directions. The ciliary microactuator array has immediate applications for positioning, alignment, inspection, and assembly of small parts, such as IC dice, with micron-scale resolution.

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.

PECVD silicon carbide as a chemically resistant material for micromachined transducers

Abstract Plasma enhanced chemical vapor deposited (PECVD) amorphous hydrogenated silicon carbide is a material with many potential applications for micromachined transducers. Specifically, its resistance to etching in a broad range of media such as sulfuric acid/peroxide, hydrofluoric acid and potassium hydroxide make it an excellent choice for use as an encapsulating material for media compatible transducers. This etch resistance also makes it useful as a masking material for intermediate processing steps. Despite this wet chemical resistance, it can be patterned easily in fluorine-based plasmas. A series of trials were undertaken in an attempt to correlate stress, resistivity and wet etch resistance with the following deposition parameters: pressure, CH4 flow rate, low frequency power, low frequency cycle time, high frequency power, and high frequency cycle time. Work to date has demonstrated a CMOS compatible, insulating thin film with a low stress (

A general-purpose system for long-term recording from a microelectrode array coupled to excitable cells

A PC-based system for acquisition and processing of data from excitable cells on a microelectrode array is described. Simple and low-cost amplification and filtering custom stages are used. A software package for processing acquired data is proposed.