James T. Andrews

Fundamental performance differences between CMOS and CCD imagers: Part II

In depth characterization of CMOS arrays is unveiling many characteristics not observed in CCD imagers. This paper is the first of a series of papers that will discuss unique CMOS characteristics related to fundamental performance differences between CMOS and CCD imagers with emphasis on scientific arrays. The first topic will show that CMOS read noise is ultimately limited by a phenomenon referred to as random telegraph signal (RTS) noise. RTS theory and experimental data discuss its creation, time and frequency domain characteristics, wide variance from pixel to pixel and magnitude on the sensors overall read noise floor. Specific operating parameters that control and lower RTS noise are identified. It is shown how correlated double sampling (CDS) signal processing responds to RTS noise and demonstrate that sub electron CMOS read noise performance is possible. The paper also discusses CMOS sensitivity (V/e-) nonlinearity, an effect not familiar to CCD users. The problem plays havoc on conventional photon transfer analysis that leads to serious measurement errors. New photon transfer relations are developed to deal with the problem. Nonlinearity for custom CMOS pixels is shown to be beneficial for lowering read noise and extending dynamic range. The paper closes with a section on the high performance CMOS array used to generated data products presented.

Large format backside illuminated CCD imager for space surveillance

The key features and performance data of a 2560/spl times/1960-pixel split-frame-transfer imager developed for space surveillance is described. The eight-port, backside illuminated charge coupled device (CCD) features 24 /spl mu/m pixels with buried blooming drains to provide 100% optical fill-factor and >1000/spl times/ overload protection from blooming. The imaging and storage registers are strapped with metal to achieve vertical transfer clock rates >400 KHz for the 61 mm long imaging register gates. The 5 million pixel array operates at 2.7 frames/s. The monolithic focal plane includes a 32/spl times/32-pixel frame-transfer imager, with a single output, which operates at 1000 frames/s. The output ports employ a floating diffusion output circuit with responsivity of 10.5 /spl mu/V/e and noise of 7e RMS at a 1.25 MHz clock rate. The imager is photocomposed employing a combination of 5/spl times/ and 1/spl times/ lithography. The photocomposition approach is described.

CMOS minimal array

A high performance prototype CMOS imager is introduced. Test data is reviewed for different array formats that utilize 3T photo diode, 5T pinned photo diode and 6T photo gate CMOS pixel architectures. The imager allows several readout modes including progressive scan, snap and windowed operation. The new imager is built on different silicon substrates including very high resistivity epitaxial wafers for deep depletion operation. Data products contained in this paper focus on sensors read noise, charge capacity, charge transfer efficiency, thermal dark current, RTS dark spikes, QE, pixel cross- talk and on-chip analog circuitry performance.

High-power CW distributed out-coupled grating surface emitting laser-amplifiers with narrow spectra and high-quality beams

We report emission of a 100 mM cw beam into a nearly-diffraction-limited spot by a grating surface emitting (GSE) laser. The distributed out-coupled master oscillator power amplifier (DOC-MOPA) produces monochromatic (933 nm) narrow linewidth (10 MHz) beams and near-ideal far-field patterns. Single wavelength operation is demonstrated to 260 mW cw.

Monolithic high-power fanned-out amplifier lasers

Monolithic fanned-out amplifier lasers (acronym: FOAL), are capable of producing high optical power, greater than 1 watt. They operate single wavelength and can be collimated to generate a nearly Gaussian beam useful for applications requiring an inexpensive compact source of coherent radiation. Examples are space communication, frequency doubling, thermal writing, optical sensing, optical interconnection, and optical computing.

Demonstration of an InGaAsP/InGaAs multiquantum well active-grating surface-emitting amplifier

The design and operating characteristics of an InGaAsP/InGaAs strained-layer multiquantum-well active-grating surface-emitting amplifier operating at a wavelength of 1.6 mu m are reported. Single-wavelength operation was obtained with 25-dB suppression of amplified spontaneous emission at 150-mW peak power output with a differential quantum efficiency of 24%. This result verifies earlier theoretical predictions that a power output per unit length of approximately 1 W/cm is feasible.<<ETX>>

Effects of an n - layer under the gate on the performance of InP MESFET's

The microwave and dc performance of Schottky barrier InP FETs where an n-layer of low carrier concentration is incorporated between the gate metal and the active layer are reported. FETs having gate dimensions of 1 µm × 200 µm and a channel length of 7 µm were fabricated. The observed gate leakage current was about 1 µA at a reverse bias of -12 V. The voltage that can be applied to the drain before breakdown was about +20 V while the gate bias was kept at -5 V. A maximum available gain of 6 dB in a microstrip circuit was measured at 9 GHz.

High‐power, single‐frequency operation of an InGaAsP/InGaAs active‐grating surface emitting amplifier at λ=1.7 μm

We have demonstrated high‐power, single‐wavelength cw operation of an InGaAsP/InGaAs strained‐layer multi‐quantum‐well active‐grating surface‐emitting amplifier operating at a wavelength of 1.7 μm. Single‐wavelength operation was obtained with 38 dB suppression of amplified spontaneous emission at 107 mW cw power output.

Deep UV sensitive high frame rate backside illuminated CCD camera developments

New applications for ultra-violet imaging are emerging in the fields of drug discovery and industrial inspection. High throughput is critical for these applications where millions of drug combinations are analyzed in secondary screenings or high rate inspection of small feature sizes over large areas is required. Sarnoff demonstrated in1990 a back illuminated, 1024 X 1024, 18 um pixel, split-frame-transfer device running at > 150 frames per second with high sensitivity in the visible spectrum. Sarnoff designed, fabricated and delivered cameras based on these CCDs and is now extending this technology to devices with higher pixel counts and higher frame rates through CCD architectural enhancements. The high sensitivities obtained in the visible spectrum are being pushed into the deep UV to support these new medical and industrial inspection applications. Sarnoff has achieved measured quantum efficiencies > 55% at 193 nm, rising to 65% at 300 nm, and remaining almost constant out to 750 nm. Optimization of the sensitivity is being pursued to tailor the quantum efficiency for particular wavelengths. Characteristics of these high frame rate CCDs and cameras will be described and results will be presented demonstrating high UV sensitivity down to 150 nm.

Coherent high-power operation of InGaAsP/InGaAs multiple-quantum-well active-grating surface-emitting amplified lasers

The design and operating characteristics of strained-layer InGaAsP/InGaAs active-grating surface-emitting amplified diode lasers are presented. For the first time, we report cw operation of an active-grating amplifier at a single wavelength of 1.7 micrometers with a cw power output in excess of 100 mW. In addition, we discuss, theoretically, the possibility of laterally scaling these devices using antiguided laser-array structures.