John Palma

Line Scanner for Biometric Applications

Fingerprints are the most common biometric measure taken, and in recent years electronic fingerprint scanning has become commonplace. Although contactless fingerprinting methods are used, it is more common that the fingerprint is taken by pressing the finger against a computer scanner. In the current study, the advantages of the contactless technique are combined with the very promising attributes of line scanning. Line scanner views each portion of the finger perpendicularly, therefore removing the projection errors of conventional flat scanning. The three dimensional image of a finger is recorded in pixel-thick lines by scanning the camera around the finger. The final image captures an uncoiled view of the finger. Emerging technology for biometric identification is based on storing the blood vessel map in the finger. We developed a system where line scanning of finger ridges in conventional light is taken as the camera goes clockwise around a finger and in the Infrared light the image of blood vessels is recorded as the camera goes back to its initial position. Line scanning also opens a new possibility in face recognition where the comparison of major anthropometric lines would help to immunize the recognition system against benign cosmetics as well as intentional efforts to defeat such systems through the use of make-up or plastic surgery.

Improving FET Switch Linearity

RF field-effect transistors, especially pseudomorphic high-electron mobility transistors (pHEMTs), are commonly used as switches in communication applications. These small high-speed devices are vital for routing and conveying signals in such uses. The important characteristics of pHEMTs, besides their small size, are their high-frequency capability, insertion loss, isolation, power handling, switching speed, and linearity. A topology using a pair of simple but modified series and shunt elements was designed to improve upon the linearity of an RF switch. Each element of the switch was composed of a single, unbiased, but relatively long pHEMT, which was designed for the test. By shifting the position of the gate asymmetrically toward the source terminal in these transistors, it was found that the linearity was improved without cost to other performance parameters

Field effect controlled lateral field emission triode

Lateral field emission transistors show promise for many high frequency and high power applications. Typical lateral devices place a gate roughly in between the cathode tip and the anode. While effective, such devices require large gate voltages for device control. This study proposes relocating the gate on top of the semiconductor cathode stem, behind its emitting tip, allowing field effect transistor based control of the transistor. Both enhancement and depletion mode are possible, and the gate bias range needed for control becomes an easily designed parameter. Example structures are modeled where this range is about 1 V. Relocation of the gate has the additional benefit of simplifying the region between the anode and the cathode tip, thus opening up the possibility of shrinking their spacing.

3D modeling of dual-gate FinFET

The tendency to have better control of the flow of electrons in a channel of field-effect transistors (FETs) did lead to the design of two gates in junction field-effect transistors, field plates in a variety of metal semiconductor field-effect transistors and high electron mobility transistors, and finally a gate wrapping around three sides of a narrow fin-shaped channel in a FinFET. With the enhanced control, performance trends of all FETs are still challenged by carrier mobility dependence on the strengths of the electrical field along the channel. However, in cases when the ratio of FinFET volume to its surface dramatically decreases, one should carefully consider the surface boundary conditions of the device. Moreover, the inherent non-planar nature of a FinFET demands 3D modeling for accurate analysis of the device performance. Using the Silvaco modeling tool with quantization effects, we modeled a physical FinFET described in the work of Hisamoto et al. (IEEE Tran. Elec. Devices 47:12, 2000) in 3D. We compared it with a 2D model of the same device. We demonstrated that 3D modeling produces more accurate results. As 3D modeling results came close to experimental measurements, we made the next step of the study by designing a dual-gate FinFET biased at Vg1 > Vg2. It is shown that the dual-gate FinFET carries higher transconductance than the single-gate device.

P1.4: Field effect controlled lateral field emission triode

Lateral field emission transistors show promise for many high frequency and high power applications. Typical lateral devices place a gate roughly in between the cathode tip and the anode. While effective, such devices require large gate voltages for device control. This study proposes relocating the gate to on top of the semiconductor cathode stem, behind its emitting tip, allowing field effect control of the transistor. Both enhancement and depletion mode are possible, and the gate bias range needed for control becomes an easily designed parameter. Example structures are modeled where this range is about a volt. Relocation of the gate has the additional benefit of simplifying the region between the anode and cathode tip, thus opening up the possibility of shrinking their spacing.

Determination of Defect Densities in High Electron Mobility Transistors Using Current Transient DLTS

Since its introduction, Deep Level Transient Spectroscopy (DLTS) has become the preferred tool for investigating semiconductor defects. The limitations of measuring the small changes in gate capacitance in transistors led to the advent of current transient DLTS where the defects manifest themselves as a small change in drain current. However, this method was introduced at a time when heterostructure devices, such as High Electron Mobility Transistors (HEMTs), were non‐existent and fails in determining defect concentrations in these modern devices. This study establishes a method by which defect concentrations can be determined in HEMT structures using current transient DLTS. First, the relationship between the change in the trap charge and the transistor drain current is established. Then, a computer aided technique is described which determines the volume within the device where the Fermi level crosses the trap energy. The result is that trap densities and their locations can be determined. DLTS measurem...

Light emission from semiconductor triode

Light emission in a novel HEMT-like structure was observed under conditions of strong reverse bias on the Schottky gate with a positive bias on the drain. Two distinct regions of light emission are present in the device with emission of red shaded light at the drain side of the gate and off-white color emission at the drain. These two distinct colors are clearly visible with the use of a microscope. The bias levels under which light emission occurs approach those necessary for catastrophic device breakdown. In the continuation of the study, spectroscopy of the emitted light is planned.