Research And Design Of Trench MOS Power Device For BMS

The importance of Battery Management System(BMS)for improving battery performance and extending battery life can be seen in different applications.For lithium ion(Li-ion)battery BMS applications in the low-voltage field,the study of Trench MOS that act as over-charge and over-discharge protection in the circuit is the focus of this thesis.The low on-state resistance and low loss of the Trench MOS is important to reduce the power consumption of the system and improve the efficiency.The main work and innovation points of thesis are as follows:1?The Novel Trench MOS(N-TMOS)uses an 8-inch process,and due to the limitation of the trench etching accuracy,the original two-dimensional direction of the source P+is changed to the Z direction for lower on-resistance requirements,thus decreasing the cell size to 0.5?m,increasing the current density compared to the conventional trench power MOS.In turn,low on-resistance is obtained.Because N-TMOS uses a phosphorus substrate,the thickness of epitaxial is selected to be 3.5?m considering the effect of substrate back-expansion.By optimizing the structural parameters and process conditions,the simulated N-TMOS has a specific on-resistance of 3.67 m?-mm~2 and a gate charge of 22.46 n C/mm~2,which is 22.6%lower than that of the sample,and the Baliga optimum value is 0.165 MW/mm~2.The final CP test results yielded an on-resistance of 2 m?,which is 41%lower than the sample at the same voltage.2?The Conventional Trench MOS(C-TMOS)fabricated by 12-inch process is still using the conventional process of etching contact holes for P+injection,and the cell size is 0.88?m,which is not sub-micron level due to the limitation of design rules.Therefore,the plate area is increased to reduce its on-resistance.The substrate material was changed to arsenic to reduce the effect of substrate back-expansion,and the epitaxial wafer thickness was reduced to 2.5?m.By optimizing the structure and process conditions,the simulated C-TMOS has a specific on-resistance of 3.255 m?-mm~2 and a gate charge of16.29 n C/mm~2,which is 43.8%lower than the sample,and the Baliga optimum value is0.233 MW/mm~2.The final CP test result yields an on-state resistance of 3 m?,which is12%lower than the sample at the same voltage.3?To solve the problem of decreased system integration brought about by the conventional trench power MOS taking a double MOS series connection to achieve bi-directional,thesis proposes two low on-resistance devices with bidirectional blocking of bidirectional conduction,the lateral bidirectional Trench MOS device(LB-TMOS)and the vertical bidirectional Trench MOS device(VB-TMOS).The advantage of the bidirectional blocking device is that a single MOS can replace the double power switching MOS of the Li-ion battery charging and discharging circuits,which can greatly reduce the overall power consumption and on-resistance.The simulation shows that the BV_s2s1and BV_s1s2 of LB-TMOS are both 12 V,and the specific on-resistance is 2.54 m?·mm~2.The BV_s2s1 and BV_s1s2 of VB-TMOS are 26 V and 24 V,and the specific on-resistance is2.72 m?·mm~2,which is 62.9%lower than that of dual N-TMOS.