Design And Modeling Of Silicon-based And Gallium-nitride-based Power Devices With Electric Field Modulation Effect

The lateral power device is the core part of the Smart Power Integrated Circuits(SPIC)and High Voltage Integrated Circuits(HVIC).One of the core issues of lateral power devices is the trade-off between the device breakdown voltage and the specific on-resistance.To optimize the performance of power devices,researchers have proposed a variety of techniques to improve the performance of lateral power devices such as field plates,RESURF,VLD,etc.In these techniques,the electric field modulation technique,which could enhance the performance of the lateral device through modulating the device surface electric field distribution by altering the device body structure parameters,has been developed as the major power device enhancement technique,and it has been applied to a variety of new structures by researchers.However,there are two problems during its application.Firstly,the analytical model for electric field modulation technology needs to be established urgently which could provide physical guidance during the new device design.Secondly,during the application of the technology,the vertical voltage endurance capability of the device is not been taken count in during the application of the electric field modulation technology,which would limit the further development of this technology.In this paper,the performance of silicon-based and Ga N-based lateral high-voltage devices with electric field modulation effect is studied.The two-dimensional electric field and potential analytic model of this type of device is achieved.An assisted depleting substrate technology is proposed to extend the vertical depletion region of the lateral power devices which could improve the device vertical voltage endurance capability,and it could modulate the device surface electric field distribution through the electric field modulation effect at the same time.As a result,the device performance is greatly enhanced:(1)The electric field and potential distribution model of the patterned buried layer SOI lateral device with electric field modulation effect is established.The model takes full account of the influence of the electric field modulation effect on the device performance with different structural parameters and the expression of the electric field modulation factor is achieved.The mechanism of how to modulate the surface electric field distribution in the drift region through changing the electric field distribution in the buried layer is explained.With the analytic model and the simulation software,the single step SOI LDMOS and the double step SOI LDMOS were analyzed at the same time,and the accuracy of the analytic model is verified.In the single step SOI device,due to the varying thickness of the buried layer,the electric field distribution in the buried layer also has a great change,and a new electric field peak is introduced in the surface of the drift region through the electric field modulation effect,which makes the surface electric field distribution more uniform.With the same drift region length,the breakdown voltage of the single step SOI LDMOS is increased by more than 50% compared with the conventional SOI LDMOS,and the specific on resistance remains the same.In double step SOI LDMOS,since the carriers could be accumulated at the step corner of the double step structure,so that the electric field modulation effect could be significantly enhanced when the amount of the accumulated carriers is big enough,which makes the breakdown voltage of the double step SOI LDMOS is increased by about 80% compared with the conventional SOI LDMOS.Based on the analytic model,the RESURF criterion of the single step SOI LDMOS and double step SOI LDMOS is obtained.And the relationships between the electric field distribution,breakdown voltage,specific on resistance and the structure parameters of the devices are discussed.(2)The analytic model of the electric field and electric potential distributions of the new Al Ga N/Ga N HEMT device with step Al Ga N epitaxial layer is established.The influence of the groove depth and the groove length on the device performance is analyzed with the achieved model and the simulation software.Since the thickness of the Al Ga N epitaxial layer is stepped,the distribution of the two-dimensional electron gas at the Al Ga N/Ga N heterojunction interface is also changed,which modulated the electric field distribution of the drift region by the electric field modulation effect,besides,a new electric field peak is introduce at the edge of the groove,which makes the drift region electric field distribution more uniform,and the breakdown voltage of the device has also been significantly improved.However,due to existence of the trench area,the two-dimensional electron gas concentration would decrease at the trench region,which leads to a higher resistance of the device.Therefore,during the device design,it was important choose a proper groove dimension to gain the required device performance.The Al Ga N/Ga N HEMTs with the threshold voltage of-1.8V were achieved by etching the Al Ga N epitaxial layer at the edge of the gate.It is found that the new structures almost have the same positive characteristics with those of the conventional device.However,the breakdown voltage is obviously improved compared with the conventional structure.At the same time,the current collapse effect of the device is released due to the optimization of the surface electric field distribution.And the device reliability is also improved due to the more uniform surface electric field distribution.(3)In order to further optimize the voltage endurance capability of lateral high voltage devices,an Assisted Depleting Substrate(ADS)technology is proposed for the first time.It could extend the vertical depletion region of the lateral power device to take full advantage of the substrate to sustain the applied voltage.With this technology,the device's vertical breakdown voltage is greatly improved,the breakdown voltage saturation limit of lateral power device is also broken.What's more,through the electric field modulation effect,the surface electric field distribution of the device is also modulated,which could further enhance the device breakdown performance.In order to fully explain the mechanism of the application of this technology in the lateral power device,a LDMOS with Assisted Depleting Substrate Layer(ADSL)is taken as an example to demonstrate the principle of ADS technology.The underlayer is formed by alternately arranging P pillars and N pillars under the drain electrode.The vertical depletion region in the substrate could be greatly expanded,and the surface electric field distribution and the vertical electric field distribution of the device are both modulated by the electric field modulation effect,which makes the electric field distribution of the device more uniform,as a result,the device's breakdown voltage is significantly improved.The results achieved with Sentaurus show that with the same drift region length of 70?m,the breakdown voltage is increased from 653 v for the conventional LDMOS to 1151 V for the ADSL LDMOS,the increment is about 76%.