Reducing an array’s pixel pitch reduces the size and weight of the focal plane array (FPA) and its associated dewar,
cooler and optics. Higher operating temperatures reduce cool-down time and cooler power, enabling reduced cooler size
and weight. High operating temperature small pitch (≤15 um) infrared detectors are therefore highly desirable. We have
characterized a large number of MWIR and LWIR FPAs as a function of temperature and cutoff wavelength to
determine the impact of these parameters on the FPA’s dark current, 1/f noise and defects. The 77K cutoff wavelength
range for the MWIR arrays was 5.0-5.6 um, and 8.5-11 um for the LWIR arrays. DRS’ HDVIP<sup>®</sup> FPAs are based on a
front-side illuminated, via interconnected, cylindrical geometry, N+/N/P architecture. An FPA’s 1/f noise is manifested
as a tail in the FPA’s rmsnoise distribution. We have found that the model-independent nonparametric skew
[(mean–median)/standard deviation] of the rmsnoise distribution is a highly effective tool for quantifying the magnitude
of an FPA’s 1/f noise tail. In this paper we show that a standard FPA’s 1/f noise varies as n<sub>i</sub> (the intrinsic carrier
concentration), in agreement with models that treat dislocations as donor pipes located within the P-volume of the unit
cell. Nonstandard FPAs have been observed with systemic 1/f noise which varies as n<sub>i</sub><sup>2</sup>.
The utilization of the non-equilibrium photodiode concept for high operating temperature (HOT) FPAs is discussed, both generically, and with regard to the specific example of MWIR HgCdTe. The issues of dark current, surface passivation, and 1/f noise are considered for three different architectures, namely N<sup>+</sup>/N<sup>-</sup>/P<sup>+</sup>, N<sup>+</sup>/P<sup>-</sup>/P<sup>+</sup>, and nBn. These architectures are examined with regard to possible FPA performance limitations, and potential difficulty in reduction to practice. Performance data obtained at DRS for the N<sup>+</sup>/N<sup>-</sup>/P<sup>+</sup> and N<sup>+</sup>/P<sup>-</sup>/P<sup>+</sup> HgCdTe architectures will be presented.
To improve its capacity to meet customer needs, DRS Infrared Technologies began technology transfer of the VOx uncooled FPA process from its Anaheim facility to its Dallas facility in the Fall of 2002. The new facility delivered its first U3000 arrays (320x240, 51μm pitch) three months after the VOx deposition system was installed, and produced over 300 units of U3000 per month just twelve months after beginning the transfer. Process enhancements and tool upgrades have enabled excellent control of the microbolometer process. Today, this line selectively fabricates arrays with NETD varying from 30mK to 80mK in 15mK bins with less than 30 ms time constant. The same arrays also have low defect density of less than 2% dead pixels and no more than one row and one column out. The arrays are packaged in imager or radiometer (F/1.4) packages. DRS also transferred small and large format arrays with 25μm pitch under the PEO-Soldier Sensor Producibility to the Dallas facility. Production of the 25μm pitch devices is currently more that 100 units per month and is ramping up to meet customer demand. This paper reports on production progress on the U3000s and the status of U3500 and U6000 25μm pitch array.
In situ monitoring provides numerous advantages in the fabrication of HgCdTe-based infrared devices. Two in situ monitoring techniques are currently being investigated in our laboratory: optical emission spectroscopy (OES) and ellipsometry. OES is ideal for end point detection, for monitoring reactor integrity, and it also provides chemical information. Ellipsometry is a technique useful for the determination of film thickness and surface roughness. Process control can be readily achieved through the implementation of these two in situ measurement techniques. Examples of the use of OES for end point detection during the plasma etching of }fgCdTe and ZnS are discussed. In situ ellips.ometry is being pursued for monitoring the mild plasma etching of bromine/ methanol polished HgCdTe surfaces prior to in situ passivation and insulator deposition. To support the utility of in si.u ellipsoriietry, our initial studies using ex situ ellipsoinetry measurements of plasma etched HgCdTe are highlighted. The advantages of in situ monitoring for multistep vacuum processing, including contamination reduction and improved process control, are presented.