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An implantable CMOS circuit interface for multiplexed microelectrode recording arrays

A second-generation multichannel probe designed for measuring single-unit activity in neural structures is described. The probe includes CMOS circuitry for electronically positioning the recording sites with respect to the active neurons and for amplifying and multiplexing the recorded signals. The probe selects eight active recording sites from among 32 on the probe shank using a static input channel selector. The neural signals on the selected channels are then amplified and multiplexed to the outside world. The probe offers a typical AC gain of 300 (15 Hz to 7 kHz), a DC gain of 0.3, and an equivalent input noise of 15 mu V rms. Operating from a single 5-V supply, the probe dissipates 2.5 mW of power and implements channel selection, self-testing, data output, and initialization using three external leads. The probe is realized using 12 masks in a high-yield single-sided dissolved wafer process with a 3- mu m feature size for the circuitry and a 3- mu m pitch on the electrode shanks. >

Scaling limitations of silicon multichannel recording probes

The scaling limitations of multichannel recording probes fabricated for use in neurophysiology using silicon integrated circuit technologies are described. Scaled silicon probe substrates 8- mu m thick and 16- mu m wide can be fabricated using boron etch-stop techniques. Theoretical expressions for calculating the thickness and width of silicon substrates have been derived and agree closely with experimental results. The effects of scaling probe dimensions on its strength and stiffness are described. The probe shank dimensions can be designed to vary the strength and stiffness for different applications. The scaled silicon substrates have a fracture stress of about 2*10/sup 10/ dyn/cm/sup 2/, which is about six times that of bulk silicon, and are strong and very flexible. Scaling the feature sizes of recording electrode arrays down to 1 mu m is possible with less than 1% electrical crosstalk between channels.<<ETX>>

An ultraminiature CMOS pressure sensor for a multiplexed cardiovascular catheter

A multiplexed ultraminiature pressure sensor designed for use in a cardiovascular catheter is described. The sensor operates from only two loads, which are shared by two sensors per catheter. The sensing chip is 350 mu m wide by 1.4 mm long by 100 mu m thick. CMOS readout circuitry at the sensing site converts applied pressure to a frequency variation in the supply current, which is detected at the end of the catheter by a microprocessor-controlled interface. The nominal pressure sensitivity is 2 kHz/fF about a zero-pressure output frequency of 2.7 MHz. This on-site circuitry contains two reference capacitors which allow external compensation for nonlinearity and temperature sensitivity and has an idle-state power dissipation of less than 50 mu W. With the transducer sealed at ambient pressure, the device can resolve pressure variations of about 3 mmHg, while vacuum-sealed devices do considerably better and should permit >

Thermally driven phase-change microactuation

This paper describes a microactuation scheme based on thermally driven liquid-vapor phase-change in a partially filled sealed cavity. A test structure for studying this system has been designed and fabricated. The cavity is 900 /spl mu/m by 900 /spl mu/m by 300 /spl mu/m in size with a thin, 600 /spl mu/m by 800 /spl mu/m grid-shaped heater located on the floor of the cavity and elevated approximately 8 /spl mu/m above it. The heater is composed of open diamond-shaped unit cells defined by 12-/spl mu/m-wide, 3-/spl mu/m-thick bulk-silicon beams, giving an overall electrical heater resistance of 3-10 /spl Omega/. Using methanol as the cavity fluid with partial filling, drive levels of 10 mW sustain a 1.2-Atm pressure rise within the cavity. Real-time measurements demonstrate a pressure response time on the order of 100 ms for an input power of 100 mW. Simulated pressure response calculations indicate the potential for an optimized response time on the order of 40 ms at this power level. >

A low-noise demultiplexing system for active multichannel microelectrode arrays

The authors report a low-noise demultiplexing system capable of reconstructing multichannel single-unit neural signals derived from multiplexed microelectrode arrays. The overall multiplexing-demultiplexing system realizes ten channels, a per-channel gain of 68 dB, a bandwidth from 100 Hz to 6 kHz, and an equivalent noise level (referred to the probe input) of 13 mu V RMS. It provides for signaling over the power supply to allow the control of on-chip probe functions such as self-testing. The interchannel crosstalk is less than 3%, and switching noise is suppressed by blanking the transition intervals. The 200-kHz probe sample clock is tracked automatically over a range of 150 to 250 kHz. Neural signals as low as 20 mu V (typically 640 mu V at the demultiplexing system input) can be reconstructed. The overall system organization is compatible with the demultiplexing of as many as 40 time-multiplexed electrode channels from a single probe data line.<<ETX>>

A scaled electronically-configurable multichannel recording array

Abstract This paper describes a multichannel microelectrode array capable of recording single-unit neural activity in the central nervous system. The probe features 32 recording sites on a scaled shank less than 50,μm wide. On-chip CMOS circuitry implements signal amplification, multiplexing, and selftesting on eight active channels selected from among the 32 sites. The circuitry has a power dissipation of 3 mW, an active area of 2.5 mm2, and requires only three external leads. It utilizes bidirectional signal transmission over the output data lead for signal output and for channel selection.

An implantable CMOS analog signal processor for multiplexed microelectrode recording arrays

A second-generation multichannel probe designed for measuring single-unit activity in neural structures is described. The probe includes CMOS circuitry for amplifying and multiplexing the recorded signals and for electronically positioning the recording sites with respect to the active neurons. The probe offers a typical AC gain of 150 (50 Hz to 10 kHz), a DC gain of 0.3, and an equivalent input noise of 13 mu V rms. Eight active recording sites are selected from among 32 on the probe shank using a static input channel selector. The probe implements channel selection, self-tuning data output, and initialization using a three-lead connection to the outside world. The probe is realized using 12 masks in a high-yield single-sided dissolved wafer process with a 3- mu m feature size for the circuitry and a 3- mu m pitch on the electrode shanks.<<ETX>>

Micromachined Silicon Microprobes For Cns Recording And Stimulation

This paper reviews the present status of multichannel silicon microprobes for use in the CNS. A wide variety of probe geometries are now available for acute studies, where high-amplitude single-unit activity can be recorded from laterally- as well as vertically-spaced sites. Similar multichannel stimulating arrays allow precisely controlled current/charge waveforms to be delivered to highly-localized areas of tissue. On-chip circuitry has been developed for these probes to permit features such as amplification, impedance buffering, multiplexing, and self-testing to be realized, while minimizing the number of external leads. The extension of present structures to chronic three-dimensional recording/stimulating systems is also underway.