HK Research On The Novel HK Power Devices

The power semiconductor device is the core of power electronics technology,which plays an important and irreplaceable role in the process of power energy transmission.Developing power devices is the best choice not only for the progress of the industry but also for energy conservation and environmental protection.In the voltage-sustained technology of power devices,the structure with the high dielectric constant?HK?insulator,which is proposed by Prof.Chen Xingbi,can optimize the electric field distribution in the drift zone,thus obtaining low specific on-resistance.The HK structure avoids the extremely high demand for charge balance in the Super-junction structure and has great potential in both lateral and vertical power devices.In fact,for the design of the novel HK power devices,the ferroelectricity,process method,dielectric constant,material size,and graphic technology should be fully considered.However,at present,most of the related research on the HK devices still stays in the theoretical design and simulation,and there is not enough experimental data for reference.In order to solve these problems,the author has carried out a series of research work on the novel HK power devices,which involves the source,influence,and application of HK.All the research work is under the guidance of Prof.Chen Xingbi and Prof.Liu Yang.The innovative contents of this dissertation are as follows:1.For the vertical power field-effect transistor utilized HK insulator?HK-VDMOS?,the conductivity degradation caused by ferroelectricity is studied for the first time.Based on the hysteresis loop of ferroelectric materials,when the HK-VDMOS is converted from the off-state to the on-state,a part of the drift zone near the HK zone is depleted due to the remanent polarization of the HK insulator.The conduction current channel is narrowed and the resistance of the drift region is increased.As a result,the conduction ability of the device shows degradation.In this paper,the ferroelectric model in the semiconductor numerical simulator is used for verifying this phenomenon.The simulation result is in good agreement with the theoretical analysis.It shows that the on-state voltage drop of the device could be increased by about 30%,due to the influence of ferroelectricity.In addition,it is found that the conduction ability of the device could be affected by the voltage value sustained in the previous off-state.2.Based on the previous conclusion,it is pointed out that ferroelectricity should be avoided during the selection of the HK materials for the power devices.After studying the spontaneous polarization principle of the perovskite materials,and the relationship between ferroelectricity and Curie temperature,SrTiO₃ is chosen as the HK material in the power devices.The preparation process includes substrate cleaning,magnetron sputtering,and annealing.Finally,the uniform SrTiO₃ thin film with a maximum thickness of 400 nm is deposited directly on the silicon substrate.In the experiment,the film samples are observed by the optical microscope and tested by SEM and XRD.With the measurement of the film capacitance,the relative dielectric constant of SrTiO₃ is calculated to be 213.4.In addition,the wet etching with 2-?m-feature is completed,which is enough for electrode contact in the HK power devices.3.Based on the experimental results of the SrTiO₃ film,this paper proposes to utilize the HK film to improve the optimized variational doping?OPTVLD?technology.Due to the weak resistance to the impurity dose deviation,the previous OPTVLD devices need high process precision,which means the difficult design and the low yield.In this paper,it is proposed that when the dose deviates,the electric displacement lines generated by the extra charge is attracted by the HK insulator.So,the peak value of the electric field in the drift region is suppressed.For the voltage-sustained structure with OPTVLD technology,the simulation result shows that the process window of P-VLD is expanded to about 1.6 times by using the SrTiO3 film.For the lateral power field-effect transistor?LDMOS?with OPTVLD technology,the process window of the buried P-VLD layer is expanded to about 1.8 times.When considering the simultaneous dose deviation of the buried P-VLD layer and N-well,the SrTiO₃ film could improve more.4.Based on the experimental results of the SrTiO₃ film,a silicon-on-insulator lateral insulated gate bipolar transistor?SOI-LIGBT?improved by HK film is proposed.Due to the HK film's attraction to the electric displacement lines,the surface electric field distribution of the drift region could be optimized.Therefore,under the same breakdown voltage,the chip area of the proposed device is reduced and its conductive ability is enhanced.In addition,the stored carriers in the drift region are decreased,so the turn-off time,as well as the turn-off loss,is reduced.The simulation result shows that,compared with the conventional SOI-LIGBT,the improved device presents the device length shortened by 15%,the on-state voltage drop reduced by 10%,the turn-off time decreased by 42%and the turn-off loss reduced by 61%.Besides,a bi-directional conducting SOI-LIGBT is proposed.The built-in thyristor helps to realize the reverse-conducting?RC?function and provides an electron extraction path during the turn-off operation.Compared to the shorted anode technology,the additional floating P-well prevents the device from working in the unipolar mode,which eliminates the snapback problem.The simulation result shows that,compared with the conventional LIGBT with an antiparallel diode,the proposed device presents the reverse recovery charge and the turn-off loss reduced by more than 30%,and the RC voltage drop decreased by about 0.1V.