title: A Micro-Machined Microphone Based on a Combination of Electret and Field-Effect Transistor.
abstract: Capacitive-type transduction is now widely used in MEMS microphones. However, its sensitivity decreases with reducing size, due to decreasing air gap capacitance. In the present study, we proposed and developed the Electret Gate of Field Effect Transistor (ElGoFET) transduction based on an electret and FET (field-effect-transistor) as a novel mechanism of MEMS microphone transduction. The ElGoFET transduction has the advantage that the sensitivity is dependent on the ratio of capacitance components in the transduction structure. Hence, ElGoFET transduction has high sensitivity even with a smaller air gap capacitance, due to a miniaturization of the transducer. A FET with a floating-gate electrode embedded on a membrane was designed and fabricated and an electret was fabricated by ion implantation with Ga(+) ions. During the assembly process between the FET and the electret, the operating point of the FET was characterized using the static response of the FET induced by the electric field due to the trapped positive charge at the electret. Additionally, we evaluated the microphone performance of the ElGoFET by measuring the acoustic response in air using a semi-anechoic room. The results confirmed that the proposed transduction mechanism has potential for microphone applications.
authors: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea. forhim13@postech.ac.kr.
authors: Kumjae
authors: K
authors: Shin
authors: Doosan infracore, dong-gu, In-cheon 401-702, Korea. junsik.jeon@doosan.com.
authors: Junsik
authors: J
authors: Jeon
authors: Department of Electrical & Computer Engineering, Johns Hopkins University, Baltimore, MD 21218, USA. jimwest@jhu.edu.
authors: James Edward
authors: JE
authors: West
authors: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea. wkmoon@postech.ac.kr.
authors: Wonkyu
authors: W
authors: Moon
keywords: MEMS microphone; electret; field effect transistor