Research On RF Loss Of Transmission Line On GaN-on-Si

GaN-on-Si heterojunction structure has the advantages of high breakdown field strength,high two dimension electron gas(2DEG)concentration,high 2DEG saturation speed,large size,low cost,and can be integrated with Si CMOS MMICs.Therefore,it has very good application prospects in radar,satellite,5G/6G RF front-end,RF energy and other microwave and millimeter wave circuits.However,compared with GaN-on-Si C,GaN-onSi wafers have higher RF losses,especially at high temperatures.This brings great challenges to the application of GaN-on-Si in microwave and mm-wave devices and ICs,especially the performance of passive transmission lines in circuits.Therefore,we need to study the generation mechanism of RF loss of transmission lines on GaN-on-Si,and use this as a basis to break through the technology of reducing the RF loss of passive transmission lines on it.In this paper,experiments and simulations are carried out on the mechanism of RF loss of the transmission line on GaN-on-(high-resistivity)HR-Si and the method of reducing RF loss of the transmission line.The research work and results are as follows:First of all,the mechanism of RF loss of transmission lines on GaN-on-HR-Si wafers at room temperature(25 °C)was studied experimentally.Firstly,the GaN-on-HR-Si wafer was etched from top to bottom using reactive ion etching(RIE)equipment.Then,the effects of the GaN buffer layer,Al GaN transition layer,Al N nucleation layer,and carriers at Al N/Si interface on the RF loss of the transmission line are studied respectively.Experimental results show that the GaN buffer layer,Al GaN transition layer,and Al N nucleation layer have little effect on the RF loss.and the RF loss mainly comes from the carriers at the Al N/Si interface.The carriers at the Al N/Si interface mainly come from the parasitic p-type conductive channel and the possible electron inversion layer.Then,through experiments,a CV ring was fabricated on Al N-on-HR-Si wafer,and the C-V characteristic curve at 10 k Hz-1 MHz was tested.After analysis,it was determined that there was no electron inversion layer at the Al N/Si interface.Therefore,it is concluded that the RF loss of the transmission line on the GaN-on-HR-Si wafer at room temperature mainly comes from the parasitic ptype conductive channel at the Al N/Si interface.Then,the mechanism of the RF loss of the transmission line on GaN-on-HR-Si wafers at high temperature(>150?)was studied experimentally.All the epitaxial layers of GaN-onHR-Si wafer were removed by RIE etching,and the RF loss of transmission lines on GaNon-HR-Si wafers with or without epitaxial layers was compared with temperature.It was found that the RF loss is mainly from The parasitic p-type conductive channel at the Al N/Si interface;and at high temperatures,the RF loss mainly comes from the intrinsic excitation of the HR-Si substrate.In addition,the conclusion has been further verified through the variable temperature contact Hall test results of the HR-Si substrate.Finally,two methods for reducing the RF loss of transmission lines on GaN-on-Si were proposed.The first method is to pre-process the epitaxial template.It is proposed for the first time to use ion implantation to implant P ions into the Al N-on-HR-Si template to reduce the conductivity of the parasitic p-type conductive channel at the Al N/Si interface and to reduce its RF loss.The experimental results show that the RF loss of CPW on the sample after ion implantation of P will be greatly reduced.At 25?,the RF loss can be reduced from 1.58 d B/mm@40 GHz to 0.40 d B/mm@40 GHz,which is a 75% reduction.The experimental results show that the ion implantation of P has a good inhibitory effect on the RF loss of the transmission line on the Al N-on-HR-Si template.Moreover,in the temperature range of25°C to 200°C,after ion implantation of P,the RF loss of the transmission line on the Al Non-HR-Si template shows a significant decrease.When the temperature is above 200?,the suppression effect on the RF loss of ion implantation P is poor.The second method is to design and upgrade the transmission line structure.An insertion ground structure is proposed to shield the influence of GaN-on-HR-Si on RF loss.First,a simulation model of GaN-onHR-Si wafers was built based on experimental data using HFSS software.Through HFSS simulation research,it is found that in the mm-wave band,the performance of CPW is better than MSL,especially when the Si substrate is thicker.By appropriately increasing the size and metal thickness of the transmission line,the RF loss of CPW can be further reduced.Then,the inserted-grounded coplanar waveguide(IGCPW)was studied through simulation.The simulation results showed that for the IGCPW with 5 ?m low dielectric constant material BCB as the dielectric layer,it has a low RF loss of 0.33 d B/mm at 94 GHz.The simulation results show that the structure has a very good suppression effect on the RF loss of the transmission line on GaN-on-HR-Si wafers in the range from room temperature to high temperature.