Wentong Zhang

Nonvolatile Multilevel Resistive Switching in

Low-energy Ar+ ion irradiation has been applied to an Au/BiFeO3/Pt capacitor structure before deposition of the Au top electrode. The irradiated thin film exhibits multilevel resistive switching (RS) without detrimental resistance degradation, which makes the intermediate resistance states more distinguishable, as compared with the nonirradiated thin film. The stabilization of resistance states after irradiation is discussed based on the analysis of the conduction mechanism during the RS, which was investigated by means of temperature-dependent current-voltage measurement from room temperature to 423 K.

\hbox{Ar}^{+}

The equivalent substrate (ES) model and the accordant optimized structure for the lateral super junction (LSJ) device are proposed in this paper. The ES, defined as the combination of the depleted substrate under the reverse voltage and the charge compensation layer (CCL) in the substrate, is treated as a whole to analyze the modulation impact of the compensation electric field ΔE on the total electric field of the LSJ. The analytical formulas for the surface electric field profiles of the LSJ are deduced from the 3-D Poisson equation and the Green function. The ES model reveals the essence and the suppression of the substrate-assisted depletion effect in the LSJ, from which the optimized substrate conditions are achieved. The optimized substrate condition allows the LSJ device featuring a similar breakdown voltage to that of the vertical super junction. Then four typical doping concentrations of the CCLs with four different compensation electric field strengths ΔEs are compared. The developed novel device with optimized CCL delivers a breakdown voltage of 301 V, realizing 157% improvement compared with the conventional LSJ with Ld=15 μm, which shows a superior performance to the LSJ devices reported. It is noteworthy that the ES model can also be used to analyze other LSJs.

Irradiated

A novel vertical field plate (VFP) lateral device with ultralow specific on-resistance (RON,sp) is proposed in this paper. The VFP surrounded by oxide is inserted in the bulk of the drift region. Compared to the surface local depletion of the conventional lateral field plate (LFP), the depletion layer of the VFP expands to the bulk of the drift region, which enhances the bulk electric field. Therefore, ultralow RON,sp is realized in the VFP device due to high drift-region doping (Nd) and short cell pitch. An analytical FP model is developed to describe the behavior of the VFP, in which the breakdown voltage (BV) and Nd are found to be proportional to the FP factor k. Then the uniform-doped VFP laterally diffused MOSs and the step-doped VFP laterally diffused MOS are proposed. The optimized device exhibits a BV of 945 V and a RON,sp of 34 mΩ·cm2 which are superior to those of similar devices and the silicon limit.

\hbox{BiFeO}_{3}

An ultra-low specific on-resistance (Ron, sp) high voltage trench SOI LDMOS based on the enhanced bulk field (ENBULF) concept is proposed. The key feature of this new device is heavily doped N/P pillars parallel to the trench oxide layer. The bulk electric field of the trench LDMOS is enhanced both in the dielectric and the silicon layer by using the N/P pillars. Firstly, the highly doped N/P pillars introduce two new electric field peaks in the bulk of the drift region, which enhances the bulk electric fields both under the drain and source. Secondly, the additional electric field of the trench oxide layer is produced by N/P pillars, leading to a shrink of the drift area. Thirdly, the enhanced dielectric layer field (ENDIF) effect of the BOX layer occurs self-adaptively with different thicknesses of the BOX layer. Combining the trench and SJ technologies, the cell pitch is reduced and the optimized doping concentration of the drift region is increased. The Ron,sp is therefore reduced efficiently. The 2-D analytical model of the ENBULF LDMOS is developed to guide the design of the novel device. Based on the model and the simulation, the ENBULF LDMOS exhibits a offstate BV of 684 V and a Ron, sp of 48.5 mΩ·cm2. The new device breaks through the silicon limit in a wide applied voltage levels.

Thin Films

A new relationship between the specific ON-resistance R_ON and breakdown voltage V_B for the balanced symmetric superjunction (SJ) device is presented to produce the lowest R_ON for a given V_B. The design formulas, including the doping density NW and the drift length L_d, are given for both the nonfull depletion (NFD) and the full depletion SJ devices with an introduction of the normalized V_B factor η. For the NFD SJ MOSFET, an R_ON ∝ V1.03 B relationship is obtained. The analytical results show good agreement with the numerical results.

Equivalent Substrate Model for Lateral Super Junction Device

The optimization methodology of the minimum specific ON-resistance RON,min for the lateral superjunction device is proposed based on the concepts of charge and potential electric fields in this paper. From the RON,min method, a new relationship between RON and breakdown voltage VB is developed, and the analytical formulas are obtained to directly give the doping concentration N and the drift length Ld. The calculated results, including the 800 and 1600 V examples, are in good agreement with the simulations. The optimized designs are also compared with the existing experimental and simulated data. It is shown that RON from the proposed optimization method is minimum, and the methodology of RON,min is universal.

A Novel Vertical Field Plate Lateral Device With Ultralow Specific On-Resistance

The global optimization of the balanced symmetric vertical superjunction (VSJ) device is proposed based on the R-well model for the first time to realize the unique minimum specific on-resistance R_ON,min. The R-well model, which is originated from our previous VSJ mode theory, shows the relationship between R_ON and the doping concentration N under the given pillar width W and breakdown voltage V_B. The global R_ON optimization is realized to obtain the design formulas of N and the pillar length Ld. The calculated results are in good agreement with the simulations. It is demonstrated from the comparisons with the simulations and the existing experiments that the optimization in this paper realizes the unique R_on,min with a relationship of R_ON ∝ V_B^1.03. The R-well model is also universal for other R_on optimizations.

Ultra-low specific on-resistance SOI high voltage trench LDMOS with dielectric field enhancement based on ENBULF concept

An optimization theory is developed for the balanced symmetric superjunction with the interface isolator layer (I-SJ) in this paper. The theory includes two parts: the electric field calculation by the Taylor series method; the design formulas by the minimum specific onresistance RON,min optimization. Based on the theory, a new I-SJ structure with a single cell is proposed, which shows the minimum RON among the superjunction (SJ) devices with the 1 μm shallow depths. RON of the new device is reduced by 53.5% compared with that of the conventional SJ lateral double diffused metal-oxide-semiconductor field effect transistor (LDMOS) and 67.6% with the conventional LDMOS under the same breakdown voltage VB of 658 V.

Theory of Superjunction With NFD and FD Modes Based on Normalized Breakdown Voltage

A 700 V self-ISO (isolated) DB-nLDMOS (dual P-buried-layer nLDMOS) without epitaxy is proposed in this paper. By separately implanting deep junction NWELLs, drift region of low doping concentration in neck region is achieved. This alleviates the concentration of the electric field and avoids premature avalanche breakdown around the birds beak. Furthermore, introduction of triple RESURF (reduce surface field) technology and optimal device sizes benefit for ultra-low Ron,sp (specific on-resistance). Finally, this ISO DB-nLDMOS is experimentally integrated in a 700 V BCD process platform. Testing results show that proposed device achieves 780-V BVds, 10.4-Ω·mm2 Ron,sp and 20-V floating voltage of source electrode.