Xenics has developed a family of stitched SWIR long linear arrays that operate up to 400 KHz of line rate. These arrays
serve medical and industrial applications that require high line rates as well as space applications that require long linear
arrays. The arrays are based on a modular ROIC design concept: modules of 512 pixels are stitched during fabrication to
achieve 512, 1024 and 2048 pixel arrays. Each 512-pixel module has its own on-chip digital sequencer, analog readout
chain and 4 output buffers. This modular concept enables a long array to run at a high line rates irrespective of the array
length, which limits the line rate in a traditional linear array. The ROIC is flip-chipped with InGaAs detector arrays.
The FPA has a pixel pitch of 12.5μm and has two pixel flavors: square (12.5μm) and rectangular (250μm). The frontend
circuit is based on Capacitive Trans-impedance Amplifier (CTIA) to attain stable detector bias, and good linearity
and signal integrity, especially at high speeds. The CTIA has an input auto-zero mechanism that allows to have low
detector bias (<20mV). An on-chip Correlated Double Sample (CDS) facilitates removal of CTIA KTC and 1/f noise,
and other offsets, achieving low noise performance. There are five gain modes in the FPA giving the full well range
from 85Ke- to 40Me-. The measured input referred noise is 35e-rms in the highest gain mode. The FPA operates in
Integrate While Read mode and, at a master clock rate of 60MHz and a minimum integration time of 1.4μs, achieves the
highest line rate of 400 KHz.
In this paper, design details and measurements results are presented in order to demonstrate the array performance.
Proc. SPIE. 9451, Infrared Technology and Applications XLI
KEYWORDS: Nonuniformity corrections, Signal to noise ratio, Detection and tracking algorithms, Cameras, Sensors, Calibration, Field programmable gate arrays, Algorithm development, Camera shutters, Temperature metrology
A shutterless algorithm is implemented into the Xenics LWIR thermal cameras and modules. Based on a calibration set and a global temperature coefficient the optimal non-uniformity correction is calculated onboard of the camera. The limited resources in the camera require a compact algorithm, hence the efficiency of the coding is important. The performance of the shutterless algorithm is studied by a comparison of the residual non-uniformity (RNU) and signal-to-noise ratio (SNR) between the shutterless and shuttered correction algorithm. From this comparison we conclude that the shutterless correction is only slightly less performant compared to the standard shuttered algorithm, making this algorithm very interesting for thermal infrared applications where small weight and size, and continuous operation are important.
SWIR imaging based on InGaAs based FPAs is well suited for passive or active day and night vision applications in different weather conditions, including surveillance, defense or fire-fighting. Xenics developed the Rufus camera, based on a 640 x 512 pixel resolution FPA. In order to achieve the best performance over a large span of lighting conditions, different smart algorithms are implemented onboard.
The auto-exposure algorithm optimizes the integration time in order to position the image histogram at a given usercontrolled brightness level. Moreover the algorithm can also switch automatically between different gain and read-out modes. At the same time a TrueNUC™ algorithm is calculating the non-uniformity correction. This correction depends on the detector temperature and integration time, because of the variable dark current of the InGaAs diodes. After the image correction and auto-exposure, further image enhancement is done by additional auto-gain and histogram equalization algorithms. Depending on the application, the user can modify several parameters of the algorithms, e.g. the maximal allowed stretching, the output histogram position and equalization strength.
In the paper we will report on the performance of the algorithms at different environmental conditions. The residual Fixed Pattern Noise (FPN) of the TrueNUC™ model is analyzed. For the TrueNUC™ implementation a typical residual FPN of <1% is obtained (at 25°C) over the complete integration time range from 100us up to 40ms, both in high and low gain. Finally we will illustrate the capabilities of the algorithms in different applications.
Xenics has designed and manufactured a 1280*1024 pixel, 17 µm pitch InGaAs array for SWIR imaging in the [0.9 - 1.7 µm] range. It will report on the first characterization results of the device. As usual for this type of room temperature operated SWIR image sensors, the detector interface is based on a CTIA stage, yielding excellent linearity, a low detector bias and hence a low and stable dark current combined with low image lag. The charge to voltage conversion factor is 40 µV/e-. The pixel interface scheme contains a CDS circuit in order to reduce the kTC noise and common mode effects. The noise is expected to be below 30 e-rms in linear mode, resulting in a dynamic range < 60 dB. Additionally the linear dynamic range is complemented with a high dynamic range logarithmic response with a saturation level < 5 nA/pixel. The information in the pixel matrix can be read via 2, 4 or 8 outputs, yielding a maximum full frame rate between 50 and 200 Hz. Each output is operating at 40 MHz pixel rate. The outputs are differential with a common mode voltage of 0.9 V and an adjustable output swing of 2 Vptp. Nevertheless the power dissipation shall be below 330 mW.
We report on the fabrication and characterization of solar blind Metal-Semiconductor-Metal (MSM) based
photodetectors for use in the extreme ultraviolet (EUV) wavelength range. The devices were fabricated in the AlGaN-on-
Si material system, with Aluminum Gallium Nitride (AlGaN) epitaxial layers grown on Si(111) by means of Molecular
Beam Epitaxy. The detectors' IV characteristics and photoresponse were measured between 200 and 400 nm. Spectral
responsivity was calculated for comparison with the state-of-the-art ultraviolet photodetectors. It reaches the order of 0.1
A/W at the cut-off wavelength of 360 nm, for devices with Au fingers of 3 μm width and spacing of 3 μm. The rejection
ratio of visible radiation (400 nm) was more than 3 orders of magnitude. In the additional post-processing step, the Si
substrate was removed locally under the active area of the MSM photodetectors using SF6-based Reactive Ion Etching
(RIE). In such scheme, the backside illumination is allowed and there is no shadowing of the active layer by the metal
electrodes, which is advantageous for the EUV sensitivity. Completed devices were assembled and wire-bonded in
customized TO-8 packages with an opening. The sensitivity at EUV was verified at the wavelengths of 30.4 and 58.4 nm
using a He-based beamline. AlGaN photodetectors are a promising alternative for highly demanding applications such as
space science or modern EUV lithography. The backside illumination approach is suited in particular for large, 2D focal