Array of silicon field effect transistors to detect charges propagation in neurons circuit
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Array of silicon field effect transistors to detect charges propagation in neurons circuit C. Delacour, G. Bugnicourt, G. Bres, T. Crozes and C. Villard Institut Néel, CNRS-Université Joseph Fourier-Grenoble INP, BP 166, F-38042 Grenoble, France.
ABSTRACT We present transport properties of silicon nanowires field effect transistors realized on SOI substrates and their application to probe electrical activity of biological objects. Devices are sensitive to short and weak voltage pulses (ms, mV) applied in an electrolyte solution, allowing a future efficient detection of neuronal activity. For that purpose, the organized growth of neuronal cells along chosen patterns has been obtained, leading to an accurate coupling with silicon nanowire field effect transistors. Both network architectures, neural and semiconducting, have been designed to study some aspects of the propagation and the processing of information by the nervous system. INTRODUCTION Silicon nanowire field effect transistors (FET) are promising tools for probing electrical activity of biological objects at the sub-cellular scale. As the detectors are non-invasive, recording the activity of the cell could be done during its growth over several days. Cell should act as a gate electrode and induced a shift of the nanowire conductance when a variation of membrane potential occurs, ie when cell is carrying information. Unlike conventional micro-electrodes (MEA), silicon nanowires are more sensitive [1], CMOS compatible for a large-scale integration and can address a smaller area (10 nm). Coupled to neurons, this allows to detect, stimulate or inhibit their electrical activity. Some proofs of concepts have already be obtained. Few years ago, a short voltage pulse related to the propagation of charges in a neuron has been detected with silicon nanowires [2]. More recently the coupling between a neuron and an array of nano-FETs has been obtained [3]. Our goal is to measure a real propagation of neuronal signals in an array of connected neurons. For that purpose, pre-defined neurons network had to be coupled with silicon nanowires field effect transistors (SiNW-FETs), which are measured in parallel. This project would help to go deeper in our understanding of the information processing by the nervous system and in a distant future would contribute to the study of abnormal neural activity involved in pathologies. RESULTS&DISCUSSION Silicon nanowires field effect transistor SOI substrates of 50 nm silicon thickness are previously doped with boron atoms. Contacts are made, on highly doped areas (1021at/cm3) by optical lithography followed by a Ti/Au bilayer deposition and a lift-off of metals. Silicon nanowires (Fig. 1) are then realized by electron beam lithography followed by an reactive ion etching step within an active area characterized by a lower doping (1015-1019at / cm3). Devices are then encapsulated with silica layer (500nm) except nanowires that are protected by a thin gate HFO2 oxide (10nm).
Figure 1. Left: silicon nanowires array designed to analyse a
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