Research On GaN-based Microwave Device And New High Breakdown Structure

GaN material has superior material properties,such as wide-bandgap,high critical breakdown electric field and high electron saturation speed and so on,making it an ideal candidate for a new generation of millimeter wave devices and power devices.In order to solve the problem of the electric field concentration at the drain edge of the gate,and to improve the breakdown voltage of the GaN based devices,the GaN-based devices with dipole layer(DL_HEMT)was optimized.The main characteristic of this device is that a dipole layer with polarization effect is introduced in the passivation layer between the gate electrode and the drain electrode,and the material for the dipole leyer we choose AlGaN.Because the introduction of the dipole layer,the 2DEG was partially depleted in the channel under the dipole layer,and the distribution of the electric field along the channel is modulated.The optimized result of DL_HEMTdevice achieved when the distance between gate electric and dipole layer LGD is 0?m,the Al content is 0.2 and the length of the dipole layer LD is 4?m.At this time the breakdown voltage BV and on-resistance RON of the GaN-based DL_HEMT devices are 1055 V and 0.424 m?·cm2,respectively,and the maximum value of the FOM is 2.62 GW/cm2.The breakdown voltage and the value of the FOM increased by 113% and 260% compared with the conventional structure.In order to improve the frequency characteristics of GaN-based devices,an AlGaN/GaN MIS-HEMT with high-K/low-K compound gate dielectric layer(CGD)was optimized.Owing to the different dielectric constants,the discontinuity of the electric field at the high-K/low-K interface can modulate the distribution of the electric field along the channel under gate,and there is a new electric field peak appeared at the high-K/low-K interface,the average drift velocity increases apparently.Hence,enhancement of DC and RF characteristics can be achieved.The optimized results of the AlGaN/GaN MIS-HEMT with CGD structure revealed that the DC transconductance gm and the maximum saturation current Ids increased about 10.5% and 6.9% compared with the traditional AlGaN/GaN MIS-HEMT with single high-K gate dielectric layer(SGD),respectively.Also,the cutoff frequency ft and the maximum oscillation frequency fmax of 74.2GHz and 129.2GHz are obtained and improved about 18.5% and 14.7% compared with the device with SGD structure.Based on the simulation of the GaN-based CGD device,we obtained that for the device with CGD structure and gate length Lg=250nm,the optimal DC and RF characteristics are obtained while the introduced low-K length l=150nm.