Fei Zhang

Novel plugged p/sup +/ collector structure for high-performance IGBT

For the first time, a novel plugged p+ collector is proposed for the insulated gate bipolar transistor (IGBT) and evaluated in detail by using two-dimensional numerical simulations as an effective method to control the collector injection efficiency and enhance the turn-off performance. Extensive simulations indicate the turn-off time of this device is reduced and the forward blocking capability is improved significantly compared to the conventional IGBT. Most importantly, the proposed IGBT breaks the deadlock between the low on-state energy loss and fast speed by engineering the whole heavy-doped p+ collector into a high-injection-efficiency heavy-doped p + region and a low-injection-efficiency lightly doped p- region to offer a more superior on-state/switching tradeoff. The heavily doped p+ region assures an optimum level of conductivity modulation required for a reasonable on-state voltage drop in the n- drift region, while the lightly doped p- region accelerates the devices turn-off. These advantages make this device an attractive candidate for high-frequency high-power applications

Adjustable high-speed insulated gate bipolar transistor

A new adjustable insulated gate bipolar transistor (IGBT) with Si/SiGe heterojunction collector structures is proposed to improve the operation speed and decrease the turnoff power loss by suppressing the tail-current. SiGe collector provides low contact resistance without consequently sacrificing turnoff losses, and also acts to suppress hole-injection into drift region during on-state and accelerate the clear sweep of the holes when the device is cutoff. On the other hand, turn-on voltage loss is increased due to the use of SiGe collector. This drawback can be minimized by using lower percentages of Ge in SiGe, since the potential barrier height at the Si/SiGe junction is controlled by the percentage of Ge in SiGe, which means the proposed IGBT can be tuned freely to meet different needs by means of changing the percentage of Ge region in the SiGe. Further, the proposed IGBT exhibits a more superior on-state/switching tradeoff relation when compared to the conventional IGBT. Two-dimensional device and circuit mixed-mode simulations are also performed to offer valuable information about the internal dynamical mechanisms of these devices, thus improving the understanding of device performance in SiGe collector applications

High Performance Polarizing Beam Splitter with Embedded Metal-wire Nanograting

Based on innovative nano-optical structures and design, an embedded metal-wire nanograting was fabricated for using as a broadband polarizer or polarizing beam splitter to reflect TE-polarized light and transmit TM-polarized light, and AR coating was designed in order to achieve best efficiency for both polarizations. An upper-cladding layer of the same material as the gratings is deposited on the ridge of the gratings, whereas the metal wire is deposited in the grating trenches. This embedded structure makes the grating firmer in its applications. By optimization of the designed structure and AR coating, high polarization efficiency and low insertion loss with a broad wavelength ranges 1000-2000 nm and a wide angular tolerance are obtained

Effective target tracking from IR image sequence

A novel TBD algorithm for tracking dim moving point target in IR image sequence with low SNR was demonstrated. Original images are preprocessed using temperature non-linear elimination and Top-hat operator, and then a composite frame is obtained by projecting operation along the time axis to reduce 3D spatio-temporal scanning for target to 2D spatial hunting. Finally the target trajectory is tracked under the condition of constant false-alarm probability (CFAR). From the experimental results, the algorithm can successfully detect dim moving point target and accurately estimate its trajectory. The algorithm, insensitive to the velocity mismatch and the changes of statistical distribution of background clutter, is adaptable to real-time target detection and tracking.