The Landsat missions are the longest continuous record of changes in the Earth's surface as seen from space. The next
follow-on activity is the Landsat Data Continuity Mission (LDCM). The LDCM objective is to extend the ability to
detect and quantitatively characterize changes on the global land surface at a scale where natural and man-made causes
of change can be detected and differentiated. The Operational Land Imager (OLI) is one of two instruments on the
LDCM spacecraft. OLI will produce science data for the reflective bands, which include 6 visible and near-infrared
(VNIR) and 3 short-wave infrared (SWIR) bands. The OLI instrument utilizes a pushbroom design with 15.5 degree
field of view. As a result, the OLI Focal Plane Array (FPA) cross track dimension is large, and the FPA is a critical
technology for the success of the mission. The FPA contains 14 critically aligned Focal Plane Modules (FPM) and
consists of 6916 imaging pixels in each of the 8 multi-spectral bands, and 13,832 imaging pixels in the panchromatic
band. Prior to integration into the FPA, the FPMs were characterized for radiometric, spectral, and spatial performance.
The Flight FPA has been built and its performance has also been characterized. In this paper, the critical attributes of the
FPMs and FPA are highlighted. Detailed description of the FPM and FPA test sets are provided. The performance
results that demonstrate compliance to the science mission requirements are presented.
The spatial response of a FPA is an important attribute of image quality. A novel test station for determining detector MTF has been developed and used on LWIR FPAs. The test station focuses an illuminated pinhole aperture onto a FPA, creating a sub-pixel spot. Total system MTF is determined by scanning the spot across the FPA. Optics MTF is measured by moving the imaged spot through focus and applying phase retrieval methods. The Optics MTF is then removed from the measured total MTF to produce the detector MTF. The technique has been applied to large area LWIR FPAs.
Amorphous silicon photodiode technology is a very attractive option for image array integrated circuits because it enables large die-size reduction and higher light collection efficiency than c-Si arrays. The concept behind the technology is to place the photosensing element directly above the rest of the circuit, thus eliminating the need to make areal tradeoffs between photodiode and pixel circuit. We have developed an photodiode array technology that is fully compatible with a 0.35 um CMOS process to produce image sensors arrays with 10-bit dynamic range that are 30% smaller than comparable c-Si photodiode arrays. The work presented here will discuss performance issues and solutions to lend itself to cost-effective high-volume manufacturing. The various methods of interconnection of the diode to the array and their advantages will be presented. The effect of doped layer thickness and concentration on quantum efficiency, and the effect of a-Si:H defect concentration on diode performance will be discussed. The photodiode dark leakage current density is about 80 pA/cm2, and its absolute quantum efficiency peaks about 85% at 550 nm. These sensors have 50% higher sensitivity, and 2x lower dark current when compared to bulk silicon sensors of the same design. The cell utilizes a 3 FET design, but allows for 100% photodiode area due to the elevated nature of the design. The VGA (640 X 480), array demonstrated here uses common intrinsic and p-type contact layers, and makes reliable contact to those layers by use of a monolithic transparent conductor strap tied to vias in the interconnect.