Semiconductor device and transistor

This disclosure provides a negative capacitance gate stack structure with a variable positive capacitor to implement a hysteresis free negative capacitance field effect transistors (NCFETs) with improved voltage gain. The gate stack structure provides an effective ferroelectric negative capacitor by using the combination of a ferroelectric negative capacitor and the variable positive capacitor with semiconductor material (such as polysilicon), resulting in the effective ferroelectric negative capacitor's being varied with an applied gate voltage. Our simulation results show that the NCFET with the variable positive capacitor can achieve not only a non-hysteretic ID-VG curve but also a better sub-threshold slope.