Design And Simulation Of 4H-SiC MESFETs With Novel Gate

4H-Si C MESFET(4H-Si C metal semiconductor field effect transistors) is a better choice of new generation in microwave and high power applications, and it shows potential electronic advantages due to its high power density and superior radio frequency performances. However, the breakdown voltage(VB) of Si C MESFET is inevitably decreased which is the effective technology to improve the drain current(Id) of the devices, that is to say, Si C MESFET has better DC characteristic and RF characteristic, but it is limit to the powerfrenqency to improve the performance of the device. It is hard to ensure high drain current and high breakdown voltage simultaneously. The increase in power density may cause the deviation for RF characteristic. Thus it need to be carefully traded off between Id and VB.In this paper, a novel structure of 4H-Si C MESFET(CG-MESFET) which has a clival gate is designed and proposed for the first time, to improve the drain current and breakdown voltage of Si C MESFET device and improve the radio frequency performance. Using the ideas of micro-elements, the CG-MESFET device structure is proposed on the basic of the MR-MESFET structure, it consists of two parts: lower part and upper part. The lower part, which is set in the channel region, is divided into strips and inserted in the channel resulting in modified channel depletion region. Using the tool of ISE-TCAD and comparing to DRMESFET and MR-MESFET, the simulation results show that this new structure can enhance the saturate drain current(Idsat) and breakdown voltage(VB), improve the cut off frequency(f T), thus, CG-MESFET has superior DC and RF performances. Below the lower gate of CGMESFET, the gate is set to the clival structure and the end point of it is under the right edge of the upper gate, it will control the horizon electronic filed and the current crowding effects at edge of depletion layer.CG-MESFET has an important characteristic parameter: End Point of Clival Gate(EPCG), its location will influence the physical parameters of CG-MESFET. This paper introduced the clival gate MESFET(CG-MESFET) structure, which based on the double recessed MESFET(DR-MESFET) structure and multiple-recessed MESFET(MR-MESFET) structures. ID increases when the EPCG moves from 1/4 to 1/2 of whole gate, but decreases when the EPCG moves from 1/2 to 1 of whole gate, and the drain current is maximum when EPCG is at 1/2 of whole gate. Thus, ID is maximum when EPCG is at 1/2 of whole gate. CG-MESFET has a larger ID that is 545 m A when EPCG is at 1/2 of whole gate, in comparison with the ID that is 370 m A, increased by 47.3% through the DR-MESFET. Compared to the DR-MESFET, the breakdown voltage of the CG-MESFET is 57.5V. So the CG-MESFET has an improvement in the max output power density. A Cgs about 0.435 p F/mm is obtained when the EPCG is at 1/2 of whole gate in the CG-MESFET structure, which is 32% and 27% smaller than that of the DR-MESFET and the MR-MESFET, respectively. And the Cgd has negative impact on the alternating current signal gain as the coupled capacitance from output port feeding back to the input signal. When the EPCG is at 1/2 of whole gate, the Cgd of the CG-MESFET is 0.221 p F/mm, which has about 21% and 23.8% decreases compared with that of the DR-MESFET and the MR-MESFET, respectively. And we can see that it has an obvious reduction. Because when the EPCG is at 1/2 of whole gate, CG-MESFET has a larger gm/Cgs ratio, so a larger f T around 15 GHz can be achieved, which is much higher than the 11 GHz of the DR-MESFET and the 12 GHz of the MR-MESFET, a larger bandwidth will be obtained. Thus, compared with DR-MESFET and MR-MESFET, the CG-MESFET will lead to superior DC and RF characteristics.