Double-gate thin film transistor with suspended-gate applicable to tactile force sensor
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Double‑gate thin film transistor with suspended‑gate applicable to tactile force sensor An Hoang‑Thuy Nguyen, Manh‑Cuong Nguyen, Seongyong Cho, Anh‑Duy Nguyen, Hyewon Kim, Yeongcheol Seok, Jiyeon Yoon and Rino Choi*
Abstract This paper presents a straightforward, low-cost, and effective integration process for the fabrication of membrane gate thin film transistors (TFTs) with an air gap. The membrane gate TFT with an air gap can be used as the highly sen‑ sitive tactile force sensor. The suspended membrane gate with an air gap as the insulator layer is formed by multiple photolithography steps and photoresist sacrificial layers. The viscosity of the photoresist and the spin speed was used to modify the thickness of the air gap during the coating process. The tactile force was measured by monitoring the drain current of the TFT as the force changed the thickness of the air gap. The sensitivity of the devices was enhanced by an optimal gate size and low Young’s modulus of the gate material. This simple process has the potential for the production of small, versatile, and highly sensitive sensors. Keywords: Mechanical sensors, Air gap, Membrane gate, Photoresist sacrifice, Tactile force sensor 1 Introduction Recently, a range of microelectromechanical systems (MEMS) have been proposed and fabricated for a range of applications. MEMS allows the miniaturization of mechanical device structures, such as sensors, transducers, and some microelectronics [1–4]. The convergence of a complementary metal-oxide-semiconductor (CMOS) and a microelectrochemical system to produce a suspended-gate metal-oxide-semiconductor fieldeffect transistor (MOSFET) with an air gap was proposed as a methodology to fabricate a new generation of sensors, with some spectacular results reported [5, 6]. A suspended-gate air gap MOSFET built on a Si channel has been reported [7, 8] but the optical and mechanical properties of silicon have limited their applications in the flexible, transparent, and wearable sensors compares to the other device structures [9, 10]. For that application, *Correspondence: [email protected] Department of Materials Science and Engineering, Inha University, Incheon 22212, South Korea
suspended-gate thin-film transistors (TFTs) with organic or inorganic semiconductors have attracted considerable attention. Zang et al, reported ultra-sensitive pressure detection sensors using organic TFTs with a spectacular suspended-gate structure with an air gap as the dielectric layer [11]. Mannsfeld et al. presented a capacitive pressure sensor with a micro-structured PDMS as the dielectric layers for an organic single-crystal transistor that exhibited unprecedented sensitivity and short response times [12]. Zang et al. reported a suspended composite gate structure with Ag nanowires, Fe3O4, and PDMS for organic transistors as flexible magnetic sensors [13]. Despite these advantages, such as great sensitivity and rapid response time in recording pressure, acoustic wave realization, and magnetic fields, thei
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