Pixel Yield Research Articles

512$\,\times\,$512 Individually Addressable MWIR LED Arrays Based on Type-II InAs/GaSb Superlattices

Single element 33×33 μm2 InAs/GaSb superlattice light-emitting diodes (SLEDs) operating at 77 K with peak emission at approximately 4.6 μm are demonstrated. A peak radiance of 2.2 W/cm2/sr was measured corresponding to an apparent temperature greater than 1350 K within the 3-5 μm band. A 48 μm pitch, 512 × 512 individually addressable LED array was fabricated from a nominally identical SLED wafer, hybridized with a read-in integrated circuit, and tested. The array exhibited a pixel yield greater than 95%.

P‐34: Active Matrix Programmable Monolithic Light Emitting Diodes on Silicon (LEDoS) Displays

AbstractIn this paper, the first full‐color active matrix programmable monolithic Light Emitting Diodes on Silicon (LEDoS) displays are fabricated using flip‐chip technology. The forward voltage uniformity of the LED pixels was greatly improved by a double‐side ground structure. A basic LED micro‐array module was fabricated and the AM substrate has scaling‐up ability. By integrating a certain number of LED micro‐array modules onto a large‐scale AM substrate, a large‐scale display is obtained. By this scaling‐up method, the utilization rate of the LED wafers is increased significantly. The yield of the LED pixels is improved simultaneously. Red, green and blue phosphors were excited by UV light to realize a full‐color display.

QWIP-based thermal infrared sensor for the Landsat Data Continuity Mission

The thermal infrared sensor (TIRS) is a QWIP based instrument intended to supplement the Operational Land Imager (OLI) for the Landsat Data Continuity Mission (LDCM) [See Landsat project description at: http://landsathandbook.gsfc.nasa.gov/handbook/handbook_htmls/chapter1/chapter1.html, [1]. The LDCM is planned to be launched in late 2012 and will continue the 35 year legacy of the Landsat program as Landsat 7 degrades. The LDCM is a joint NASA–US Geological Survey (USGS) mission. The TIRS instrument is a far infrared imager operating in the push broom mode with two IR channels: 10.8 μm and 12 μm. The focal plane will contain three 640 × 512 QWIP arrays mounted on a silicon substrate. The readout integrated circuit (ROIC) is intended to be the Indigo 9803. The focal plane operating temperature will be 43 K (nominally). Bandpass filters will define the precise spectral response of the focal plane. Two QWIP designs will be pursued, the corrugated structure and the grating structure. NASA/Goddard, the Army Research Lab and QmagiQ will work closely together to obtain the suite of arrays that will best meet the mission requirements (primarily adequate conversion efficiency at the required wavelengths). This paper will describe the design and fabrication of the TIRS instrument with particular emphasis on the QWIP detectors. The QWIP parameters that are driving the mission requirements include spectral response, dark current, conversion efficiency, read noise, temperature stability, pixel uniformity and pixel yield. Additional mechanical constraints such as co-registration between the three arrays, filter design and assembly and testing will also be discussed.

A novel TFT‐OLED integration for OLED‐independent pixel programming in amorphous‐Si AMOLED pixels

Abstract— The direct voltage programming of active‐matrix organic light‐emitting‐diode (AMOLED) pixels with n‐channel amorphous‐Si (a‐Si) TFTs requires a contact between the driving TFT and the OLED cathode. Current processing constraints only permit connecting the driving TFT to the OLED anode. Here, a new “inverted” integration technique which makes the direct programming possible by connecting the driver n‐channel a‐Si TFT to the OLED cathode is demonstrated. As a result, the pixel drive current increases by an order of magnitude for the same data voltages and the pixel data voltage for turn‐on drops by several volts. In addition, the pixel drive current becomes independent of the OLED characteristics so that OLED aging does not affect the pixel current. Furthermore, the new integration technique is modified to allow substrate rotation during OLED evaporation to improve the pixel yield and uniformity. The new integration technique is important for realizing active‐matrix OLED displays with a‐Si technology and conventional bottom‐anode OLEDs.

Lead chalcogenide on silicon infrared sensors: focal plane array with 96×128 pixels on active Si-chip

The first monolithic 2D narrow gap infrared focal plane array on a Si-substrate, where the Si contains the active addressing electronics, has been realized. It consists of 96×128 photovoltaic Pb/PbTe sensors for the 3–5 μm range. The pixels are electronically addressed row-by-row and the columns are read-out in parallel. Pixel yield was up to above 98%, quantum efficiencies around 60%, and mean differential resistances 4 M Ω at 100 K. The noise current is correlated with the dislocation density in the epitaxial layer.

A compact 64-pixel CsI(Tl)/Si PIN photodiode imaging module with IC readout

We characterize the performance of a complete 64-pixel compact gamma camera imaging module consisting of optically isolated 3 /spl times/ 3 /spl times/ 5 mm/sup 3/ CsI(Tl) crystals coupled to a custom array of low-noise Si PIN photodiodes read out by a custom IC. At 50-V bias, the custom 64-pixel photodiode arrays demonstrate an average leakage current of 28 pA per 3 /spl times/ 3 mm/sup 3/ pixel, a 98.5% yield of pixels with <100 pA leakage, and a quantum efficiency of about 80% for 540-nm CsI(Tl) scintillation photons. The custom 64-channel readout IC uses low-noise preamplifiers, shaper amplifiers, and a winner-take-all (WTA) multiplexer. The IC demonstrates maximum gain of 120 mV/1000 e/sup -/, the ability to select the largest input signal in less than 150 ns, and low electronic noise at 8-/spl mu/s peaking time ranging from 25 e/sup -/ rms (unloaded) to an estimated 180 e/sup -/ rms (photodiode load of 3 pF, 50 pA). At room temperature, a complete 64-pixel detector module employing a custom photodiode array and readout IC demonstrates an average energy resolution of 23.4% FWHM and an intrinsic spatial resolution of 3.3-mm FWHM for the 140-keV emissions of /sup 99m/Tc. The construction of an array of such imaging modules is straightforward; hence this technology shows strong potential for numerous compact gamma camera applications, including scintimammography.

Uncooled thin film infrared imaging device with aerogel thermal isolation: deposition and planarization techniques

We have successfully integrated a thermally insulating silica aerogel thin film into a new uncooled monolithic thin film infrared (IR) imaging device. We have calculated noise equivalent temperature differences of 0.04–0.10°C from a variety of PbxZryTi1−yO3 (PZT) and PbxLa1−xZryTi1−yO3 (PLZT) pyroelectric imaging elements in these monolithic structures. The low thermal conductivity of the aerogel films should also result in a significantly faster temporal response as well. Fabrication of these monolithic devices entails sol–gel deposition of the aerogel, sputter deposition of the electrodes, and solution chemistry deposition of the pyroelectric element. Consistent pyroelectric response across the device is achieved by use of appropriate deposition and planarization techniques of these three layers. Adjusting the chemistry and deposition process of the aerogel thin film had the greatest effect on large-scale uniformity and performance across the device. Sputter depositing a planarization layer on top of the aerogel offered only minimal improvement in reducing surface roughness. However, using solution chemistry to deposit multiple thin coatings of PZT for the imaging element resulted in a visible reduction in scattering and 80–100% pixel yield.

The vertical photoconductor: A novel device structure suitable for HgCdTe two-dimensional infrared focal plane arrays

A novel photoconductive device structure is proposed and described that has been designed specifically as a sensing element for high density two-dimensional infrared focal plane array (IRFPA) applications. Although the design concept can be applied to a variety of epitaxially grown HgCdTe material, optimum performance can be achieved using n-type HgCdTe semiconductor material consisting of epitaxially grown heterostructure layers in which a two-dimensional mosaic of vertical design photoconductors are fabricated. The heterostructure layers provide high performance devices at greatly reduced power dissipation levels, while the vertical design allows for the high density integration of photoconductors in a two-dimensional array geometry with high fill factor. The salient feature of the proposed device structure is that the bias field is applied in the vertical direction such that it is parallel to the impinging infrared radiation. A comprehensive one-dimensional model is presented for the vertical design photoconductor, which is subsequently used to determine the optimum design parameters in order to achieve maximum responsivity at the lowest possible power dissipation level. It is found that the proposed device structure has the potential to be used in the fabrication of long wavelength IRFPAs approaching 10 6 pixels using 25 × 25 μm 2 detector elements. Furthermore, this is achieved with individual device detectivities that are background limited and for a total array power dissipation of less than 0.1 W using a pulsed biasing scheme. Performance issues such as response uniformity, pixel yield, fill factor, crosstalk, power dissipation, detector impedance, array architecture, and maximum array size are discussed in relation to the suitability of the proposed vertical photoconductor structure for use in IRFPA modules. When considering IRFPA operability, it is found that in many cases the proposed technology has the potential to deliver significant advantages, such as higher yield, higher fill factor, better uniformity, less crosstalk, and larger potential array size, when compared to photovoltaic technology.