Design And Research Of Silicon Based RF LDMOS Devices

RF LDMOS device as the core of power integrated circuits,in recent years,it has become a research hotspot for large number of domestic and foreign device researchers,because of the serious contradiction between the breakdown voltage and the on-resistance in the transverse high-voltage power device,the application of RF LDMOS in high voltage and high current environment has been restricted.At the same time,with the rapid development of civil mobile communication technology and military radar technology,the quality of wireless signal transmission and transmission quality is becoming higher.In the mobile communication base station and military radar,RF power amplifier is a key component in the signal transmitter,which directly determines the quality of the wireless signal receiving and transmission distance,and the performance of the RF power amplifier and its core components--RF power transistors are closely related.So now the research direction for the RF device is mainly focused on the design and manufacture of RF power devices with more superior performance,let the device has higher breakdown voltage,higher frequency and lower power consumption,this thesis is based on the development of RF LDMOS devices.Firstly,the basic working principle of the device is studied.Then,the effects of various parameters of the device on the breakdown characteristics,output characteristics and frequency characteristics of the device are analyzed by using the simulation software ISE-TCAD.Finally,based on the above work,the structure of RF LDMOS devices is optimized to make it more superior.Firstly,a new structure of RF LDMOS device with partial stepped buried layer is presented,in this structure,the SOI buried layer inside the device is stepped to modulate the surface electric field of the device,the structure of the step is optimized so that the transverse electric field distribution of the device tends to be uniform to improve breakdown voltage of the device,while the stepped SOI buried layer is used to reduce the source-drain parasitic capacitance within the device,and furtherly cut-off frequency and output power of the device are improved.Through the simulation analysis with software ISE-TCAD simulation,the surface electric field distribution model prensented in this paper is consistent with the simulation results,and the acquisition of the new electric field peak explains the modulation effect of the buried oxygen layer on the surface electric field.The device can make full use of the electric field modulation effect of the stepped SOI layer and improve the breakdown voltage of the device when the specific resistance of the device is not increased.Compared with the same size PSOI RF LDMOS device,the breakdown voltage increases from 100.1V to 123.2V,which is improved by 23.08%,and the cut-off frequency f _T of the device is increased by 18.09%because the step buried layer reduces the parasitic capacitance of the device.Secondly,this paper also presents a folded RF LDMOS on silicon substrate with drift region electrodes,this device is on the basis of the FALDMOS device,the structure of the device is added with an oxide electrode on the drift region,and a certain voltage is applied to the electrode.On the basis of the low on resistance of the FALDMOS device,do it in this way the structure can be used to increase the transconductance of the device,and further improve the characteristic frequency of the device,so that RF LDMOS devices can be well developed in the field of high frequency and low power consumption.The simulation results show that the on-resistance of silicon folded RF LDMOS devices with the drift region of the electrode compared with FALDMOS increased by 6.2%,but compared with the same size of RF LDMOS its still decreased by 36.24%,at the same time,the characteristic frequency of the device reaches 1.17GHz,which is 2.2 times of the FALDMOS device,and is 1.95 times of the ordinary RF LDMOS device.If this device is used in the RF power amplifier circuit,it can not only ensure the low power consumption of the device,but also has good frequency characteristics.