Being implemented as an active component in the circuits, two dimensional (2D) transition metal dichalcogenide (TMD) transistors have two kinds of difficulties. First, regardless of carrier type, threshold voltage (V_th) of TMD 2D field effect transistors (FETs) is located far away from 0 V. Second, gate bias induced hysteresis exists in general 2D TMD transistors, causing an unstable operation of FETs. Here, we have fabricated stable n-channel MoSe₂ FETs with a relatively small V_th of -5 V and minimized-hysteresis of 0.5 V. And we have checked the stable operation by integrating a smart touch sensor circuit composed of piezoelectric P(VDF-TrFE) polymer, the MoSe₂ FET, and organic light emitting diode (OLED). To minimize the V_th and gate voltage hysteresis of 2D FET, we inserted ultrathin (8.46 nm) polystyrene (PS)-brush layer between MoSe₂ channel and 50 nm-thin Al₂O₃ dielectric. Our MoSe₂ FET has showed a maximum drain-current (I_D) of ~9 μA at V_DS of 1 V along with a high linear mobility of 11.2 cm²/Vs. In the analogue touch sensor circuit gated by piezoelectric film of large scale Al/50 μm-thick P(VDF-TrFE)/ITO/glass, the MoSe₂ FET exhibites high ON/OFF ratio and ON-state I_D which quite well demonstrated OLED pixel operation.