Investigation of in-situ doping profile for N+/P/N+ bidirectional switching device using Si_1−xGe_x/Si/Si_1−xGe_x structure

Abstract

We present a novel junction device with bidirectional current flow for switching devices in a high density spin torque transfer magnetic random access memory (STT-MRAM). In this structure, an N+ type strained SiGe material is adopted as a conduction layer to generate higher electron mobility and a flatter doping profile. A SiGe/Si/SiGe heterojunction structure is also used to obtain a better I_on/I_off ratio due to a steeper junction profile. It is confirmed by 3D simulation that this structure provides higher current drivability and I_on/I_off ratio. After the simulation, a junction device with N+ Si_0.8Ge_0.2/P Si/N+ Si_0.8Ge_0.2 and an area of 4 × 4 um² is fabricated and evaluated for bidirectional current flow. From the results obtained, we propose that this bidirectional switching device with a heterojunction structure is a promising candidate for a high density STT-MRAM.