Yourun Zhang

The effect of the surface recombination on current gain for 4H-SiC BJT

Two-dimensional analysis of the surface recombination on current gain for 4H-SiC BJT (bipolar junction transistor) is studied. The experiment is well-matched with the simulation result, which is modeled by the continuous interface state distributions replacing the single interface state trap. The mechanism of current gain degradation is discussed.

The preparation of two inch double-sided YBCO thin films

The preparation of two inch double-sided YBCO thin films by simultaneous sputtering from a single target is reported. The lateral homogeneity of microwave surface resistance of the YBCO thin films, on both sides of the two inch wafer, is characterized by using a Fabry?Perot resonator at 145 GHz and 75 K. Values of microwave surface resistance Rs (75 K, 145 GHz, 0 T) below 55 m? were reached over the whole area of YBCO thin films on two inch LaAlO3 wafers. The majority of the wafer area has Rs (75 K, 145 GHz, 0 T) values in the range of 15 m? to 40 m?. The uniformity of Rs values in the whole two inch wafer is excellent and the properties of YBCO thin films were found to be very similar on both sides of the wafer.

Analysis of thermal characteristics of current gain for BJT-BSIT compound device

Analytical thermal characteristics of current gain for BJT-BSIT (bipolar junction transistor-bipolar static induction transistor) compound device in the low current operation is proposed. The author makes the thermal model and also obtains a best thermal compensating factor of the compound device that indicates the relationship between the thermal rating of current gain with device structure parameters. It is important for the better design of compound device. At last, the analytical model is found in good agreement with numerical simulation and experimental results. The test results demonstrate that the thermal rating of current gain is less than 10% in 25degC-85degC and 20% in -55deg-25degC.

The dielectric properties of pulsed laser deposited SrTiO 3 thin films

Dielectric thin films of SrTiO3 (STO) were deposited on Y1Ba2Cu3O7-x (YBCO) HTSC bottom layer by PLD method. X-ray diffraction results show that thin films were well crystallized and highly oriented in the (100) direction. Parallel capacitors were fabricated to investigate the low frequency dielectric properties of STO films. The current-voltage (I-V) characteristics indicated that a Shottcky barrier exist at the interface between STO films and YBCO films. Dielectric dissipation of STO capacitor showed large frequency dispersion under high electric fields. It was explained by the space charge polarization near the interface.

High current gain 4H-SiC BJT for limiting surface states effect

In this paper, a novel 4H-SiC BJT is proposed to obtain a high current gain by separating electron and hole near the SiC/SiO2 surface. It is effective to improve the current gain by extending the emitter metal to overlap the passivation layer on the extrinsic base which modulates the surface potential. Compared with the conventional BJTs, the surface recombination rate decreases and the current gain improves by 63.2% with the compatible process technology. The optimized size is oxide layer thickness in the order of 50 nm and overlapping metal length in the order of 4 μm.

Static and dynamic study in high-voltage 4H-SiC PiN rectifiers

Designing and fabrication of 4kV, 20A 4H-SiC PiN diodes with JTE junction termination structure have been investigated in this paper. A bevel mesa structure and a single-zone junction termination extension (JTE) have been employed to achieve the target voltage. Finally, an optimized mesa structure without sub-trench (mesa height of 2.2 µm and mesa angle of 20°) has been experimentally demonstrated. A forward voltage drop of 3.5 V at 100 A/cm2 are obtained from the fabricated diodes. Furthermore, capacitance and reverse recovery switching performance are presented. The value of capacitance under 800V reverse voltage is about 48pF. Subsequently, the reverse recovery of the fabricated PiN rectifiers at different forward current and different switching rates is demonstrated.

High current gain 4H-SiC bipolar junction transistor

A novel 4H-SiC BJT of high current gain with a suppressing surface traps effect has been proposed. It is effective to improve the current gain due to the lower electrons density in the surface region by extending the emitter metal to overlap the passivation layer on the extrinsic base surface. The electrons trapped in the extrinsic base surface induce the degeneration of SiC BJTs device performance. By modulating the electron recombination rate, the novel structure can increase the current gain to 63.2% compared with conventional ones with the compatible process technology. Optimized sizes are an overlapped metal length of 4 μm, as well as an oxide layer thickness of 50 nm.

Novel 4H‐SiC BJT utilizing floating buried layer in base for high current gain, high current gain stability and high breakdown voltage

Purpose – The purpose of this paper is to present a novel structure of 4H‐SiC bipolar junction transistor (BJT) to realize high current gain, high current gain stability, and high breakdown voltage.Design/methodology/approach – A novel structure of 4H‐SiC BJT with floating buried layer in the base epilayer is presented. The simulation and optimization are done using the TCAD tool.Findings – This novel structure is increasing the current gain effectively, at the same time, the current gain stability and breakdown voltage are higher comparing with the conventional structure.Originality/value – The paper proposes a new “4H‐SiC FBL‐BJT” with high current gain, high current gain stability and high breakdown voltage.

Novel structure of 4H-SiC bipolar junction transistor

A novel structure of 4H-SiC bipolar junction transistor (BJT) with floating buried layer (FBL) in the base epilayer is presented. Numerical simulations are performed to demonstrate that the current gain shows an approximately 100% increase due to the creation of buried layer electric-field. However, the variation rate of current gain is decreased sharply indicating FBL structure with high current gain stability due to reducing the recombination current of base-emitter depletion region. Furthermore, the charges in the buried layer modulate the electric-field resulting from a higher electric-field peak introduced at the etched edge of base-collector junction, which results in breakdown voltage (BVCEO) enhanced.