Macroporous Silicon Sensor Arrays for Chemical and Biological Detection
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MACROPOROUS SILICON SENSOR ARRAYS FOR CHEMICAL AND BIOLOGICAL DETECTION Jeffrey Clarkson, Vimalan Rajalingam, and Karl D. Hirschman Departments of Microelectronic Engineering and Materials Science & Engineering, Rochester Institute of Technology, Rochester, NY 14623
Huimin Ouyang, Wei Sun and Philippe M. Fauchet Departments of Biomedical Engineering and Electrical & Computer Engineering, University of Rochester, Rochester, NY 14642 ABSTRACT A new class of silicon-based chemical and biological sensors that offer an electrical response to a variety of substances is described. The devices utilize silicon flow-through sensing membranes with deep trench structures formed to depths up to 100µm, fabricated by electrochemical etching which transforms the silicon into macro-porous silicon (MPS). The sensors have demonstrated the ability to detect the presence of certain chemical and biological materials. Although the principle of operation of the devices is fairly complex, the transduction mechanisms can be compared to chemiresistors and chemically sensitive field-effect transistors (chemFETs). The electrical responses that have shown the most sensitivity are AC conductance and capacitance. Previous work has demonstrated that upon exposure to organic solvents (i.e. ethanol, acetone, benzene) the devices exhibit a characteristic impedance signature. The devices have also shown the ability to detect the hybridization of complementary DNA. The incorporation of other materials that have demonstrated sensitivity to low ambient levels of contaminants is also under investigation. The sensors have been designed and fabricated in linear array configurations; a microfluidic transport chip/package co-design is currently in progress. INTRODUCTION There have been several types of gas and chemical sensors developed, each with their own specific advantages and disadvantages in performance with respect to sensitivity, selectivity, power consumption, size, cost, and applications (Ref. 1 provides a thorough review). Chemi-resistors and ChemFETS are among the available solid-state devices that have advantages over other classes (e.g. optical) in size and portability, but continue to have issues related to selectivity and sensitivity [1]. With the increased emphasis on homeland security, the ability to detect biological materials has become increasingly important. Although electronically integrated microarrays for DNA analysis have been developed, commercial technologies rely primarily on off-chip optical detection / readout platforms [2]. Integrated optical detection schemes have been implemented [3], although the system complexity increases significantly. Electrical readout schemes are currently being developed [4], which offer significant advantages in system integration. Silicon has been demonstrated to be promising as a biocompatible material [5], and has an unmatched capability to provide a platform for integrated electronics and mechanical structures. There have also been numerous reports of porous silicon applications in chemic
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