Heterogeneous Integration of Analog CMOS Chips on Flexible Substrates for High-resolution Deep Brain Epilepsy Diagnosis☆

A device capable of recording single unit activity (SUA) deep within the brain is presented in this work. A high-channel count of 128 is achieved by integrating CMOS signal processing capability inside the cylindrical device with a diameter of 1 mm. The probe uses planar photolithography to pattern the high-resolution metal tracks on a polyimide foil, which is later converted into the cylindrical shape of deep brain probes through the use of dedicated tools and an innovative molding process. The purpose of the integrated circuitry is to pre-process the recorded neural signals so that it can be time-domain multiplexed onto only 8 output leads, thereby reducing the interconnection effort at the end of the probe. The functionality of the device is confirmed by characterizing the contact resistance of the interface between the CMOS chips and the substrate. Furthermore, the CMOS electronics have been tested. The signal conditioning front-end produces a gain of 100, band limits the signal to 10 kHz, and generates an input referred noise of 8 mu V-rms while consuming 12 mu W/channel. Impedance measurements confirm the electrical functionality of the electrode sites. (C) 2015 The Authors. Published by Elsevier Ltd.