AbstractsEngineering

The nervous system communicates and processes information through its basic structural units  – individual neurons (nerve cells). Neurons convey neural information via electrical and chemical signals, which makes electrophysiological recording techniques very important in the study of neurophysiology. Specifically, active microelectrode arrays (MEAs) with amplifiers integrated on the same substrate are used because they provide a very powerful neural electrical recording technique that can be directly interfaced to acute slices and cell cultures. 2D planer electrodes are typically used for recording from neural cultures in vitro, while in vivo recording in live animals invariably requires the use of 3D electrodes. I have designed an active MEA with neural amplifiers and 3D electrodes, all integrated on a single chip. The electrodes are commercially available 3D C4 (Controlled Collapse Chip Connect) flip-chip bonding solder balls that have a diameter of 100 µm and a pitch of 200 µm. An active MEA neural recording chip  – the Multiple-Input Neural Sensor (MINS) chip  – was designed and fabricated using the IBM BiCMOS 8HP 0.13 µm technology. The MINS IC has 256 input channels that are time-division multiplexed into two output pads. Each channel was designed to work at a 20 kHz frame rate with a total voltage gain of 60 dB per channel with an input-referred noise voltage of 5.3 µVrms over 10 Hz to 10 kHz. The entire MINS chip has an area of 4 x 4 mm^2 with 256 input C4s plus 20 wire-bond pads on two adjacent edges of the chip for power, control, and outputs. The fabricated MINS chips are wire-bonded to standard pin grid array (PGA), open-top PGA, and custom-designed printed circuit board (PCB) packages for electrical, in vitro, and in vivo testing, respectively. After process variation correction, the voltage gain of the 256 neural amplifiers, measured in vitro across several chips, has a mean value of 58.7 dB and a standard deviation of 0.37 dB. Measurements done with the electrical testing package demonstrate that the MINS IC has a flat frequency response from 0.05 Hz to 1.4 MHz, an input-referred noise voltage of 4.6 µVrms over 10 Hz to 10 kHz, an output voltage swing as large as 1.5 V peak-to-peak, and a total power consumption of 11.25 mW, or 43.9 µW per input channel.