A study on the magnetic sensitivity of sectorial split-drain magnetic field-effect transistor

Abstract

Due to the high demand of magnetic sensors in the market nowadays, CMOS magnetic sensor sectorial SD-MAGFETs become widely used because of their compact size and their compatibility with the standard CMOS technology. In order to make better use of sectorial SD-MAGFETs, the lateral interface charge effect, and the scaling effect is applied to it to analyze the magnetic sensitivity change. The other parameters such as the source sector angle α are also varied to show the geometric dependent magnetic sensitivity I especially investigated to address the problem of lateral Si/SiO2 interface traps of the sectorial SD-MAGFETs. Due to its special structure and its exposure to the magnetic field, the interface traps at the lateral sidewall of the channel will affect its performance. Consider complex geometry of the device, both theoretical analysis and simulation validations are provided. The interface traps are studied by different types, trap density, and trap energy level of the interface traps and their impact on the magnetic sensitivity of the sectorial SD-MAGFET. The acceptor- type traps are negatively charged when filled with electrons and magnetic sensitivity is increased by increasing IH and decreasing IDS. On the other hand, the donor-type traps are positively charged when filled with electrons and magnetic sensitivity is decreased by decreasing IH and increasing IDS. Acceptor trap energy level lies near to the valance band and the donor trap energy level lies near to the conduction band will also make the magnetic field increase. The analytical model of Hall current IH is first time proposed and shown that it is exponential decay with the time stressing and the decay rate is proportional to the fill rate of the interface traps. This proves there exists the lateral interface traps in the sectorial SD-MAGFET experimentally. The fill rate of the traps at the channel boundary is also source sector angle α dependent. The most serious deterioration of the magnetic sensitivity is observed with α = 56º. Transient sensing hysteresis and magnetic sensing dynamic range are further investigated by experiments and analytical model with charge trapping effect are proposed. Under the increasing magnetic field, the magnetic sensitivity will be affected by the interface charge trapping effect and magnetic sensitivity is inverse quadratic proportional to the source sector angle α. However, the largest magnetic sensitivity, sensing hysteresis and the largest magnetic dynamic range are achieved with different α. As a result, simulation and experimental results both provide design insights of the sectorial SD-MAGFETs. The performance of sectorial SD-MAGFETs can be improved to shrink the channel length into 0.486 μm, as high as the magnetic sensitivity 8.06 %/T is achieved. Considerable results are included to fulfil a comprehensive study on the scaling down of the sectorial SD-MAGFET. The research conducted in this thesis will provide important information for the engineer to design and process the sectorial SD-MAGFETs in the future.