Analysis of Poly-Si and Metal Contact Characteristics in Reconfigurable MOSFETs

Abstract

A poly-Si reconfigurable Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are fabricated and the device operation is successfully demonstrated. Poly-Si MOSFETs are very efficient in terms of channel characterization of poly-Si RFETs with programmable bottom gate arrays because of their simple fabrication steps. By changing the bottom-gate bias, the electrical doping characteristics of the channel can be converted to electrical n-/p- type channel. When the bottom-gate is negative, the channel becomes electrically p-type channel. On the other hand, when the bottom-gate is positive, the channel becomes electrically n-type channel. The oxide and active channel thickness are important factors in device performance, such as current level, because they relate to gate controllability. The thinner the oxide and active channel thickness, the better performance of the device. To obtain high Ion and symmetric operation, ohmic-like contact is necessary for both n- and p-type operations. Since Al and NiSi are mid-gap metals for intrinsic silicon, both metals are investigated as am-bipolar Source/Drain contact metal. The devices using Al deposited by thermal evaporator and sputter as a contact metal are annealed at 350oC for 10 min to remove native oxide. After annealing the device with Al contact, the device with short channel (≤1μm) is short. Other devices using NiSi as contact metal are silicided at various temperatures for 1 min to form nickel silicide after depositing Ni by sputter. The best silicide condition is 450oC for 1min. Among these various contact metals (Al, NiSi) and annealing conditions, the best condition for the symmetric operation is NiSi at 450oC for 1min. Additionally, the poly-Si reconfigurable MOSFETs having top-gate can be operated as n-/p-MOSFET. The top-gate configures the device polarity (n- or p-MOSFSET) and the bottom-gate is used as a control gate. . The Ion for the n-/p-MOSFET operation with a single poly-Si reconfigurable MOSFETs reach up to 32/0.9μA for Al contacts, respectively.