Semiconductors & Integrated Circuits : Switches

Semiconductors & Integrated Circuits Portfolios


All-Glass Optical Microresonator for Single Molecule Spectroscopy and More

Building on their previous work, the researchers have developed all-glass microtoroidal resonators with improved sensitivity (i.e., superior Q/V ratio). Unlike their SiO2 on Si counterparts, the new resonators can be made chip scale – a significant advantage. Moreover, the use of glass in place of silicon makes the platform more desirable for applications including label-free sensing due to optical transparency in the visible region. Additionally, glass is a robust, chemically inert material and more biocompatible than silicon.

The new fabrication method follows the same general scheme as the previously developed oxide-on-silicon toroids, but the materials are inverted. This results in a silicon toroid atop an oxide pillar, followed by thermal oxidation to form an all-glass structure in the final step.

Microcavity Method for Single Molecule Spectroscopy

Specifically, the researchers have developed a new microcavity-based method for single molecule/particle spectroscopy. In essence, when an individual molecule or particle lands on the microcavity surface, it absorbs energy from a free space pump laser beam and generates heat. The heat is transferred to the microcavity, causing a shift in resonance frequency and therefore detectable changes in the light (e.g., power or intensity).

The superb sensitivity of the method enables detection, identification and real-time analysis of single molecules and particles. This is exciting because current spectroscopy techniques are limited to matter in the 10 to 100 nanometer size range, such as nanoparticles and viruses.

Tuning Optical Microcavities

The researchers have developed a tuning method for ultrahigh-Q toroidal optical microcavities capable of rapid modulation and resonance position control.

In the new configuration, a free-space pump laser beam illuminates the pillar supporting the microcavity, which warms ups and transfers heat to the microcavity. This induces a shift in resonance frequency. The support pillar is made of silicon or other suitable material.

The intensity of the free-space laser beam can be adjusted by changing the power and/or focal spot of the beam. Different intensities are used to achieve the desired shift in resonance frequency.

Method to Manage Active Leakage Power in Power Gated Integrated Circuits

UW–Madison researchers have developed an improved leakage power management technique using programmable power gating transistors. The method addresses the problems of oversized PG devices and active power leakage by changing the number of active power gating transistors as a function of usage-time and temperature to decrease leakage current when the PG transistors are in the on or wake state.

An integrated circuit includes multiple PG transistors connected in parallel that selectively control power to the integrated circuitry according to a sleep/wake signal used for power conservation. A transistor aging detector generates a signal reflecting aging of the power gating transistors. This signal controls the PG transistors to compensate for a decrease in PG transistor current flow as the PG transistors age. The PG transistors have different control inputs connected to the sleep/wake signal and the transistor-aging detector increases a number of control inputs connected to the sleep/wake signal as the PG transistors age. The technique decreases unnecessary leakage current early in the life of an integrated circuit by avoiding the need to oversize the PG transistors to accommodate end-of-life-cycle degradation of the transistors. As a result, supply voltage may be better tailored to minimize current leakage when the integrated circuit is young or operating at low temperatures.

Flexible Germanium Lateral PIN Diodes and 3-D Arrays for Photodetector Applications

UW-Madison researchers have developed a flexible lateral PIN diode made of germanium for photodetector applications.  The flexibility of the diode gives it the unique ability to be formed into flexible two- or three-dimensional arrays.  Each diode is composed of a flexible layer of single-crystalline germanium on top of a flexible substrate.  The middle of the single-crystalline semiconductor is the intrinsic (I) semiconductor layer, which is disposed laterally between an N- and a P-type doped region.  These individual diodes are shaped like irregular polygons and can be formed into hemisphere shaped arrays. 

The arrays can be used in photodetector applications such as digital cameras, solar cells or LADAR devices, and the individual diodes can be used for electronic switch applications.  Digital cameras can use the arrays to capture light at its natural incident angle instead of bulky and expensive lenses that focus the light.  Omnidirectional, three-dimensional LADAR systems for military surveillance applications can be formed by creating a hemispherical array made up of numerous vertical cavity light emitting sources, each surrounded by the photodetector diodes.  The individual flexible, lightweight diodes also can be used in high-frequency switching applications where their flexibility is desired.  These diodes have the advantage of utilizing high-performance active components while still incorporating low-cost plastic substrates.

Nanoelectromechanical Switch in Co-Planar Waveguide

UW-Madison researchers have developed a co-planar waveguide that uses a NEMSET electromechanical signal switch for signal modulation. The NEMSET switch acts as a natural communication pathway between co-planar elements of co-planar waveguides. The device operates in the frequency range of 1MHz to 2GHz to filter, modulate, mix and rectify microwave signals. This waveguide could be used in the same way as a traditional waveguide in electrical engineering, but with the benefits of NEMSET and a co-planar structure.

Micromechanical Phase-Shifting Gate Optical Modulator

UW–Madison researchers have developed a phase shifting gate (PSG) that, instead of using micromirrors, exploits interference effects to create a highly reflective surface. This device eliminates the alignment problems present in the micromirror system.

High Performance Active Gate Drive for IGBTs

UW–Madison researchers have developed an active gate drive circuit for driving high power IGBTs that incorporates three separately controlled stages. The new design optimizes switching performance for turn-on, turn-off and all operating conditions.

The circuit includes a semiconductor switch connected in series with a low resistance gate turn-on or turn-off resistor between the voltage supply line and the gate input line, and a parallel connected bipolar transistor. After receiving a turn-on signal, the switch provides low resistance rapid charging to the gate during a first stage, controlled current charging during a second stage and, thirdly, a rapid, low resistance final charging while the signal is present. Turning off the IGBT follows a similar pattern for discharging.

Short Circuit Protection of Power Switching Devices

UW–Madison researchers have developed a high power semiconductor switching device with a gate terminal that controls current flow between the power terminals of the device. A first fault signal is provided if the current flow path of the device exceeds a selected level; similarly, a second fault signal is triggered if the voltage across the power terminals exceeds a given level. When either the first or second fault signal is provided, the gate terminal is limited to a selected control level, which intermediates the full-on and full-off current levels of the switching device.