Petre Alexandrov

Demonstration of the first 10-kV 4H-SiC Schottky barrier diodes

This letter reports the demonstration of the first 4H-SiC Schottky barrier diode (SBD) blocking over 10 kV based on 115-/spl mu/m n-type epilayers doped to 5.6 /spl times/ 10/sup 14/ cm/sup -3/ through the use of a multistep junction termination extension. The blocking voltage substantially surpasses the former 4H-SiC SBD record of 4.9 kV. A current density of 48 A/cm/sup 2/ is achieved with a forward voltage drop of 6 V. The Schottky barrier height, ideality factor, and electron mobility for this very thick epilayer are reported. The SBDs specific-on resistance is also reported.

4H-SiC normally-off vertical junction field-effect transistor with high current density

4H-silicon carbide (SiC) normally-off vertical junction field-effect transistor (JFET) is developed in a purely vertical configuration without internal lateral JFET gates. The 2.1-/spl mu/m vertical p/sup +/n junction gates are created on the side walls of deep trenches by tilted aluminum (Al) implantation. Normally-off operation with blocking voltage V/sub bl/ of 1 726 V is demonstrated with an on-state current density of 300 A/cm/sup 2/ at a drain voltage of 3 V. The low specific on-resistance R/sub on-sp/ of 3.6 m/spl Omega/cm/sup 2/ gives the V/sub bl//sup 2//R/sub on-sp/ value of 830 MW/cm/sup 2/, surpassing the past records of both unipolar and bipolar 4H-SiC power switches.

Fabrication and characterization of 11-kV normally off 4H-SiC trenched-and-implanted vertical junction FET

This letter reports the first demonstration of 101 kV trenched-and-implanted normally off 4H-SiC vertical junction field-effect transistor (TI-VJFET) with a 120 /spl mu/m /spl sim/4.9/spl times/10/sup 14/ cm/sup -3/-doped drift layer. Blocking voltages (V/sub B/) of 10 kV to 11 kV have been measured. The best specific on-resistance (R/sub SP/_/sub ON/) normalized to source active area has been determined to be 130 m/spl Omega//spl middot/cm/sup 2/. Three-dimensional computer modeling including current spreading effect shows that the TI-VJFET would have a specific resistance of 168 m/spl Omega//spl middot/cm/sup 2/ if it is scaled up substantially in size.

Fabrication and Characterization of High-Current-Gain 4H-SiC Bipolar Junction Transistors

This paper reports on newly developed high-performance 4H-SiC bipolar junction transistors (BJT) with improved current gain and power handling capabilities based on an intentionally designed continuously grown 4H-SiC BJT wafer. The measured dc common-emitter current gain is as high as 70, the specific ON-state resistance (RSP-ON) is as low as 3.0 mOmegamiddotcm2, and the open-base breakdown voltage (VCEO) reaches 1750 V. Large-area 4H-SiC BJTs with a footprint of 4.1 times 4.1 mm have been successfully packaged into a high-gain (beta = 50.8) high-power (80 A times 700 V) all-SiC copack and evaluated at high temperature up to 250degC. Small 4H-SiC BJTs have been stress tested under a continuous collector current density of 100 A/cm2 for 24 h and, for the first time, have shown no obvious forward voltage drift and no current gain degradation. Numerical simulations and experimental results have confirmed that simultaneous high current gain and high open-base breakdown voltage could be achieved in 4H-SiC BJTs.

A high current gain 4H-SiC NPN power bipolar junction transistor

This work reports the development of high power 4H-SiC bipolar junction transistors (BJTs) by using reduced implantation dose for p+ base contact region and annealing in nitric oxide of base-to-emitter junction passivation oxide for 2 hours at 1150/spl deg/C. The transistor blocks larger than 480 V and conducts 2.1 A (J/sub c/=239 A/cm/sup 2/) at V/sub ce/=3.4 V, corresponding to a specific on-resistance (R/sub sp on/) of 14 m/spl Omega/cm/sup 2/, based on a drift layer design of 12 /spl mu/m doped to 6/spl times/10/sup 15/cm/sup -3/. Current gain /spl beta//spl ges/35 has been achieved for collector current densities ranging from J/sub c/=40 A/cm/sup 2/ to 239 A/cm/sup 2/ (I/sub c/=2.1 A) with a peak current gain of 38 at J/sub c/=114 A/cm/sup 2/.

1.88-

The SiC trenched-and-implanted vertical junction field-effect transistor (TI-VJFET) is an excellent device for power switching applications, but its on-resistance needs to be further reduced to suppress ON-state power loss. In this paper, we used small cell pitch size and high channel/drift layer doping concentration to achieve low on-resistance. Advanced fabrication processes, such as Bosch process trench etching, self-aligned Ni silicide, and self-aligned gate overlay were implemented to support such an aggressive design. Normally on 4H-SiC TI-VJFETs of various channel-opening dimensions have been designed and fabricated based on a 12 mum, 1.8 times 1016 cm-3 doped drift layer. Record high performance TI-VJFETs have been achieved and will be reported. Other SiC VJFET structures under active research are reviewed and compared to TI-VJFET. Without the need for epi-regrowth or stringent lithography alignment, TI-VJFET has the advantage of a less demanding fabrication process. In addition, its high current density, adjustable channel width and low gate resistance make TI-VJFET an excellent device for fast power switching applications.

\hbox{m}\Omega\cdot\hbox{cm}^{2}

Abstract In this paper, the temperature coefficient of 4H-SiC NPN BJT current gain is studied by way of numerical simulations. In general, 4H-SiC NPN BJT would have a positive temperature coefficient (PTC) for the common emitter current gain if the acceptor ionization energy is smaller than 170 meV. Both PTC and negative temperature coefficient (NTC) can occur in 4H-SiC NPN BJT with an aluminum-doped base. High base doping concentration is required to obtain a wide range of current density with a NTC for current gain, especially when the electron lifetime in base is low. For a base doping concentration of 2.5×10 17 cm −3 , the NTC for current gain is obtained for current density up to 300 A/cm 2 , even when the electron lifetime is as low as 48 ns. The experimental results are also reported.

1650-V Normally on 4H-SiC TI-VJFET

A 4H-SiC normally off vertical channel lateral reduced-surface electric-field (RESURF) junction field-effect transistor (JFET) with a blocking voltage Vbr of 1028 V and a specific on-resistance R on-sp of 9.1 mOmegamiddotcm2 has been experimentally demonstrated. The device has a Vbr 2/Ron-sp figure-of-merit of 116 MW/cm2, which is the highest value achieved to date on a 4H-SiC lateral power transistor. Also reported is a larger JFET that is capable of handling over 0.5-A current on an active area of 4.01times10-3 cm2. The fabricated double-RESURF devices have a vertical channel length of 1.8 mum, created by tilted aluminum (Al) implantation on the sidewalls of deep trenches, and a lateral drift-region length of 7.5 mum. In addition, low-voltage logic-inverter circuits based on the same lateral JFET process have been monolithically integrated on the same chip. Proper logic-inverter function has also been demonstrated

On the temperature coefficient of 4H-SiC BJT current gain

This letter reports a newly achieved best result on the specific ON-resistance (R/sub SP/spl I.bar/ON/) of power 4H-SiC bipolar junction transistors (BJTs). A 4H-SiC BJT based on a 12-/spl mu/m drift layer shows a record-low specific-ON resistance of only 2.9 m/spl Omega//spl middot/cm/sup 2/, with an open-base collector-to-emitter blocking voltage (V/sub ceo/) of 757 V, and a current gain of 18.8. The active area of this 4H-SiC BJT is 0.61 mm/sup 2/, and it has a fully interdigitated design. This high-performance 4H-SiC BJT conducts up to 5.24 A at a forward voltage drop of V/sub CE/=2.5 V, corresponding to a low R/sub SP-ON/ of 2.9 m/spl Omega//spl middot/cm/sup 2/ up to J/sub c/=859 A/cm/sup 2/. This is the lowest specific ON-resistance ever reported for high-power 4H-SiC BJTs.

1000-V 9.1-

This letter reports the demonstration of a 4H-SiC trenched and implanted vertical-junction field-effect transistor (TI-VJFET). The p/sup +/n junction gates are created on the sidewalls of deep trenches by angled Al implantation, which eliminates the need for epitaxial regrowth during the JFET fabrication. Blocking voltages up to 1710 V has been achieved with a voltage supporting drift layer of only 9.5 /spl mu/m by using a two-step junction termination extension. The TI-VJFET shows a low specific on-resistance R/sub ON-sp/ of 2.77m/spl Omega/cm/sup 2/, corresponding to a record high value of V/sub B//R/sub ON-sp/ equal to 1056 MW/cm/sup 2/.