Dual Common Planes for Time Multiplexing of Dual-Color QWIPs

NASA Tech Briefs, Aug 2006

With external control, commercial single-color readout integrated circuits could be used.

NASA's Jet Propulsion Laboratory, Pasadena, California

A proposed improved method of externally controlled time multiplexing of the readouts of focal-plane arrays of pairs of stacked quantum-well infrared photodetectors (QWIPs) that operate in different wavelength bands is based on a dual-detec tor-common-plane circuit configuration. The method would be implemented in a QWIP integrated-circuit chip hybridized with a readout integrated-circuit (ROIC) chip.

There are alternative methods of multicolor readout, but they involve more on-chip circuitry and the attendant disadvantages of greater size, power dissipation, number of control signals, and complexity of circuitry on the QWIP and ROIC chips. To minimize size of, and power dissipation in, a multicolor pixel, one must minimize the number of transistors and control signals; this can be achieved only by time multiplexing of colors in each pixel. The time multiplexing can be controlled by signals from external or internal circuitry. The proposed reliance on external control for time multiplexing would make it possible to use a commercial single-color ROIC with only minor modifications in the form of extra metallization for an additional detector common plane and for clocking bias potentials. (If, instead, one were to rely on internally controlled multiplexing, it would be necessary to radically redesign the ROIC, at considerably greater development cost.) Other advantages of the external-control approach over the internal-control approach are greater flexibility and the possibility of using a technique, known as "skimming," for subtracting unwanted dark-, background-, and noise-current contributions from readout signals

The figure schematically depicts the circuitry in one pixel according to an internally controlled multiplexing scheme and according to the proposed externally controlled multiplexing scheme. In both schemes, the time multiplexing would be accomplished by switching (clocking or ramping) the biases applied to the QWIPs via detector common planes. In the internal-control case, a bias signal would be applied via a single detector common plane and two internal electronic switches. In the proposed external-control case, bias signals would be applied via two detector common planes, without internai electronic switches. A previously unmentioned advantage of the external-control scheme shown in the figure is the need for only one indium bump (instead of two) in each pixel.

This work wax done fry Sir R. Rafol, Sarath Gunapala, Sumith Bandara, John Liu, and Jason Mumolo of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Semiconductors & ICs category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should he addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak Grove Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: iaoffire@jpl. nasa.gov

Refer to NPO-30523, volume and number of this NASA Tech Briefs issue, and the page number.