Joining their technological skills and strengths, SOFRADIR and ULIS merged in a new High Tech Company named LYNRED. This new company will be oriented towards excellence in II-VI, III-V and bolometers technologies, covering all Society’s needs in term of infrared detection. Nowadays one noticeable trend in infrared market sensors is the optimization of two key metrics: sensor range and image quality. These metrics depend mostly on three criteria: modulation transfer function (MTF), Noise Equivalent Temperature Difference (NETD) and Residual Fixed Pattern Noise (RFPN). MTF improvement was previously achieved by reducing pixel pitch to 30μm [1] to 10μm [2]. NETD and RFPN were improving thanks to a better material quality. The improvement of NETD and RFPN can also be used to increase the operating temperature. The Modulation Transfer Function performance is directly linked to the ability to distinguish objects details and sharpness of the imaging system. MTF value determines, with NETD and RFPN, the system range via the so -called Minimum Resolvable Temperature Range (MRTD). We need to keep in mind that not only MTF has to be optimized but also MRTD, which is very challenging in the context of High Operating Temperature (HOT) and pixel pitch reduction. There are many challenges to be addressed for future small pitch, large format and HOT+ (> 160K) detectors. Electrical and optical crosstalks are one of the prime concerns for detectors with sub-10μm pixel pitch. We will compare several existing materials and their optical and electronic transport properties, elementary sensors designs, such as III-V superlattice, II-VI materials, MESA, loophole, planar and depleted photodiodes. This discussion will be based on measurements on improved HgCdTe 10μm and 7.5μm pitch technology completed by simulation using Finite Element Modelization (FEM) coupled with Finite Difference Time Domain (FDTD).
SOFRADIR is a worldwide leader on the cooled infrared (IR) detector market for high-performance space, military and security applications thanks to a high maturity Mercury Cadmium Telluride (MCT) technology, and III-V technology: InGaAs, and QWIP quantum detectors. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. The current trend in quantum IR detector development is the design of very small pixel, operating at higher temperatures. In this context, keeping high image quality is a key challenge. This paper discusses the relevant criteria to quantify image quality: the Modulation Transfer Function (MTF) and the Residual Fixed Pattern Noise (RFPN). State of the art relevant performances for IR detection and imaging will be presented for Daphnis MW product, 10μm pitch XGA/HD720 extended MW matrix (cut-off wavelength 5.3μm) operating at 110K: range improvement, digital ROIC optimization, NUC (Non Uniformity Correction) table stability. Projections and results for smaller pixel pitch are also detailed.
The remarkable properties (internal gain larger than 100 and close to unity excess noise factor) of Short Wave Infrared
(SWIR) HgCdTe electron-initiated Avalanche Photodiodes (e-APDs) are put to good use to demanding applications, i.e.
spectroscopy and LIDAR. Knowing the requirements of both situations, we have designed specific models based on
highly sensitive single elements APDs and adapted proximity electronics.
On one hand, we use the e-APDs low noise equivalent power (NEP) at 180K (few fW/Hz1/2). We simultaneously
designed a specific Transimpedance Amplifier (TIA) which allows us to take advantage of the low APD NEP. The
combination of both elements along with a dedicated cryostat enables direct LIDAR detection at moderate bandwidth
(BW = 20 MHz) without the need for long time averaging, which is crucial in far field (≥ 5 km) analysis. One the other
hand, we have optimized a low-noise and low-frequency LN2 cooled prototype operating with an external commercial amplifier. It allows us to observe the photoluminescence of Ge nanostructures in the range 1.5-2.5 μm with a
significantly increased SNR along with a reduce pump laser power. The possibility to use these detectors in the photon
counting limit will be discussed in light of our recent results. In parallel, we present preliminary time response
measurements performed on SWIR APD suggesting that a higher GHz BW could be reached with this type of detector.
This is however subjected to optical optimization at the moment.
KEYWORDS: Avalanche photodetectors, Mercury cadmium telluride, Readout integrated circuits, Mid-IR, Sensors, Short wave infrared radiation, Single photon, Electrons, Photodetectors, Signal to noise ratio
Proportional photon detection has been demonstrated using linear mode HgCdTe avalanche photodiodes (APDs)
hybridized on a specially designed read-out integrated circuit (ROIC). The ROIC was designed to detect photons at a
moderate bandwidth (10 MHz) with a low noise of 10 electrons per characteristics time of the ROIC and to be
compatible with large area-small pixel focal plane array (FPA) applications. Proportional photon counting was
demonstrated by reproducing the Poisson statics for average photon number states ranging between m=0.8 to 8 photons,
at low to moderate avalanche gains M=40-200, using both mid-wave infrared (MWIR) and (short-wave infrared) SWIR
HgCdTe APDs. The probability distribution function of the gain was estimated from the analysis of the amplitude of
detected residual thermal photons in the MWIR APDs. The corresponding probability distribution functions was
characterized by a low excess noise factor F and high asymmetry which favours a high photon detection efficiency
(PDE), even at high threshold values. An internal PDE of 90 % was estimated at a threshold level of 40 % of the average
signal for a single photon. The dark count rate (DCR) was limited by residual thermal photons in the MWIR APD to
about 1 MHz. A geometrical and spectral filtering of this contribution is important to achieve the ultimate performance
with MWIR detectors. In this case, the DCR was estimated by interpolation to about 8 kHz. The SWIR HgCdTe APD
device had a lower residual photon flux (60 kHz), but was found to be limited by tunnelling dark current noise at high
gains at a rate of 100 kHz.
Three-dimensional (3-D) flash light detection and ranging (LADAR) imaging is based on time of flight (TOF) measurement of a single laser pulse. The laser pulse coming back from the observed object will be detected only if the number of photons received by each pixel generates a signal greater than the pixel noise. In order to extract this weak photonic signal from the noise we use the high gain and low excess noise of the HgCdTe avalanche photodiode (APD) arrays developed at CEA/LETI. The sensor consists of a 30-μm pitch APD detector array hybridized to a 320×256 pixels ROIC for passive and active imaging. In passive mode the focal plane array behaves like a thermal imager and we measured 30 mK of noise-equivalent temperature difference. In active imaging mode, each pixel sensed the time of flight and the intensity two-dimensional (2-D) of a single laser pulse. Laboratory tests show a range noise of 11 cm for 4300 photoelectrons per pixel and detection limit under 100 photoelectrons. The sensor was also used during a field trial to record 2-D and 3-D real-time videos. The quality of the images obtained demonstrates the maturity of HgCdTe-APD-array technology.
CEA-Leti has developed a dual mode infrared array detector for passive (thermal) or active 2D and 3D imaging. Very
high sensitivity in 3D mode of operation is achieved by using an HgCdTe avalanche photodiode array with linear gain.
The 30 μm pitch detector array is hybridized to a 320x256 pixels Readout Integrated Circuit (ROIC). In passive mode,
the 3.6x106 e- well capacity and the low noise of the ROIC allow to reach photon noise limited NETD. For active
imaging mode, each pixel measures the time of arrival (3D) and the intensity (2D) of one laser pulse. A sensor based on
a detector array with a cut off wavelength of 4.6μm at 80K was fabricated and tested. This paper describes the pixel
architecture and presents ranging performances obtained in laboratory conditions. The first 2D and 3D active videos
obtained during a field trial of our focal plane array are presented.
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