Screen-Grid Field Effect Transistor for sensing Bio-Molecules
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Screen-Grid Field Effect Transistor for sensing Bio-Molecules. Kwee G Eng1, Kristel Fobelets1 and Jesus E Velazquez-Perez2 1
Department of Electrical and Electronic Engineering, Imperial College London, Exhibition Road, SW7 2AZ London, UK 2 Departmento de Fisíca Aplicada, Universidad de Salamanca, Edificio Trilinüe, Pza de la Merced s/n, E-37008 Salamanca, Spain ABSTRACT A novel field effect transistor, based on the Screen Grid Field Effect Transistor concept, is proposed with an integrated Coulter Counter pore for amplification of the sensing signal. 3D TCAD (Technology Computer Aided Design) simulations are performed on the use of the Coulter Counter Field Effect Transistor (CC-FET) to detect the Influenza A virus. The gate of the transistor is the pore through which the bio-particles pass. This passage causes a change in the electrostatic conditions of the gate and thus changes the source-drain current, similar to ISFET (Ion Sensitive FET) operation. The structure of the CC-FET is optimized for bio-sensing and multi-particle passage through the gate hole is simulated. TCAD results show that the CCFET is capable of multi-particle and particle size detection. INTRODUCTION Improved healthcare is a key objective in modern society. Medical diagnostic systems play an important role to establish quickly and accurately the underlying causes of an illness. A wide range of biosensors [1] have been and are being developed including the ISFET (Ion Sensitive Field Effect Transistor) [2] and Coulter Counter [3], both relevant to this work. Biosensors determine the number and type of extremely small bio-particles, e.g. red blood cells, viruses, etc. Research on the Coulter counter (CC) has seen a revival recently because of the improved control of the pore size and homogeneity via synthetic pores fabricated with microelectronics technology [4]. CCs consist of a membrane with a small pore through which the bio-particles distributed in an ionic liquid pass. Each time this happens, a sudden change in current or voltage is measured. These signals are small in amplitude and noisy. Signal processing techniques can be employed for optimizing the signal. In this work we propose to integrate the CC with a Field Effect Transistor (FET) in order to improve the signal by combining the CC and FET response. We investigate, using TCAD (Technology Computer Aided Design) [5] the operation of this integrated device. This combined CC-FET (Coulter Counter - Field Effect Transistor) structure will also open the possibility of densely packed integrated sensing arrays. In order to understand the functioning of the CC-FET, we introduce the principle of the Screen-Grid Field Effect Transistor (SGrFET). The SGrFET [6] has a completely novel gating structure that is composed of metal/oxide filled vacuoles in the Si channel of a FET on SOI (silicon-on-insulator). The vacuoles are from the top of the SOI to the buried oxide layer. Their inner surface is covered with a gate oxide and then further filled with metal. The principle of operation
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