The fast development of nitrides has given the opportunity to investigate AlGaN as a material for ultraviolet detection. Such AlGaN based camera presents an intrinsic spectral selectivity and an extremely low dark current at room temperature.
Firstly, we will present results on focal plane array of 320x256 pixels with a pitch of 30μm. The peak responsivity is around 280nm (solar-blind), 310nm and 360nm. These results are obtained in a standard SWIR supply chain (readout circuit, electronics).
With the existing near-UV camera grown on sapphire, the short wavelength cutoff is due to a window layer improving the material quality of the active layer. The ultimate shortest wavelength would be 200nm due to sapphire substrate. We present here the ways to transfer the standard design of Schottky photodiodes from sapphire to silicon substrate. We will show the capability to remove the silicon substrate, and etch the window layer in order to extend the band width to lower wavelengths.
SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons
sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the
opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space
(earth observation), transport (automotive safety) or industry (non destructive process control).
InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes
a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current
level induced by high quality material.
For few years, III-VLab has been studying InGaAs imagery, gathering expertise in InGaAs material growth and imaging
technology respectively from Alcatel-Lucent and Thales, its two mother companies. This work has lead to put quickly on
the market a 320x256 InGaAs module, exhibiting high performances in terms of dark current, uniformity and quantum
efficiency.
In this paper, we present the last developments achieved in our laboratory, mainly focused on increasing the pixels
number to VGA format associated to pixel pitch decrease (15μm) and broadening detection spectrum toward visible
wavelengths. Depending on targeted applications, different Read Out Integrated Circuits (ROIC) have been used. Low
noise ROIC have been developed by CEA LETI to fit the requirements of low light level imaging whereas logarithmic
ROIC designed by NIT allows high dynamic imaging adapted for automotive safety.
Through collaboration between III-V Lab and CEA-Leti, a 640 x 512 InGaAs image sensor with 15 μm pixel pitch has
been developed. Based on a thinned substrate, the photodiode array detects the light from the visible to the near infrared
wavelength (0.4 to 1.7 μm) with a dark current lower than 18 fA per pixel at room temperature. The readout IC (ROIC)
design in a standard CMOS 0.18 μm technology is presented. The pixel circuit is based on a capacitive transimpedance
amplifier (CTIA) stage with two selectable charge-to-voltage conversion gains. The input stage has been optimized for
low noise performance in the high gain mode. In this mode, the charge-to-voltage conversion factor is 17.6 μV/electron
and the full well capacity is above 105 x 103 electrons. The integration time can be set up to the frame period thanks to a
rolling shutter approach. The frame rate can be up to 120 fps or 60 fps if the Correlated Double Sampling (CDS)
capability of the circuit is enabled. The readout noise measured in CDS with short exposure time is around 30 electrons
for a dynamic range of 71 dB in high-gain mode and 108 electrons and 79 dB in low-gain mode.
Thanks to the high transmission coefficient of short infrared wavelengths in the atmosphere and specific contrasts, SWIR
imaging is an attractive technology for space applications such as astronomical or earth observation. Detection module
must demonstrate high uniformity, sensitivity and resolution combined with compactness to meet the needs of this
application field.
Image sensors based on InGaAs photodiodes arrays present very low dark currents even at ambient temperature as high
quality materials can be grown on InP substrates. Besides, the suppression of InP substrate after hybridization is a way to
extend the detection range towards visible wavelengths. These properties result in a new generation of sensitive, compact
and multifunctional InGaAs detection modules.
In this paper, we describe the performances of an uncooled VGA InGaAs module recently developed. The 640x512 array
with a pitch of 15μm allows high resolution images. The excellent crystalline quality induces very low dark current
densities at ambient temperature. The readout circuit is based on a capacitive trans-impedance amplifier with correlated
double sampling resulting in low readout noise figure. This compact module appears as a serious alternative to the
existing technologies for low light level imaging in the [0.4μm-1.7μm] spectral range.
SWIR image sensors based on p-i-n photodiodes arrays present a tremendous interest in applications often requiring a
high intra-scene dynamics. This paper describes a single-chip InGaAs SWIR camera with more than 120 dB intrinsic
operational dynamic range with an innovative CMOS ROIC technology initially developed by New Imaging
Technologies for visible CMOS camera chip. A simplified camera with on chip fixed pattern noise correction is
presented. We also present the next generation of focal plane arrays (FPA) based on a VGA format of 640 x 512 pixels
with a pitch of 15 μm. These FPAs are associated to a logarithmic wide dynamic range ROIC. We give the electro-optics
performances and particularly the visible extension capabilities. This InGaAs VGA logarithmic single-chip camera
allows a high resolution SWIR camera with minimized system complexity and low power consumption.
Short-wavelength infrared image sensors based on p-i-n photodiode arrays present a tremendous interest in applications such as passive and active imagery for laser detection/warning, hot spot or detection for lasers sensors, enhanced vision systems or low light level sensors. The capability to work at room temperature with dark current equivalent to silicon-based devices is another motivation for the fast development of this technology. This paper presents several modules and camera based on InGaAs photodiode arrays from the III-VLab. First, we describe the electro-optics performance in terms of dark signal, sensitivity, and particularly the visible extension capability. We also present a nucless logarithmic sensor based on a 1/2 video graphics array (VGA) format at a pitch of 25 μm initially designed for visible CMOS camera chip. We will also present the next generation of focal plane arrays based on a VGA format of 640×512 pixels with a pitch of 15 μm. This array will be associated to a CTIA readout circuit and also to an innovative CMOS logarithmic wide dynamic range ROIC, developed by New Imaging Technologies. This VGA logarithmic device developed for automotive safety will involve visible extension capability in a European project named 2Wide_sense.
This paper describes a single-chip InGaAs SWIR camera with more than 120dB instant operational dynamic range with an
innovative CMOS ROIC technology, so called MAGIC, invented and patented by New Imaging Technologies. A 320x256-
pixel InGaAs 25μm pitch photodiode array, designed and fabricated by III-Vlab/Thales Research & Technology(TRT), has
been hybridized on this new generation CMOS ROIC. With NIT's MAGIC technology, the sensor's output follows a precise
logarithmic law in function of incoming photon flux and gives instant operational dynamic range (DR) better than 120 dB.
The ROIC incorporates the entire video signal processing function including a CCIR TV encoder, so a complete SWIR
InGaAs camera with standard video output has been realized on a single 30x30 mm2 PCB board with ¼ W power
consumption. Neither TEC nor NUC is needed from room temperature operation. The camera can be switched on and off
instantly, ideal for all the portable battery operated SWIR band observation applications.
The measured RMS noise and FPN noise on the prototype sensor in dark conditions are 0.4 mV and 0.27 mV respectively.
The signal excursion from pixel is about 300mV over the 120 dB dynamic range. The FPN remains almost constant over the
whole operation dynamic range. The NEI has been measured to be 3,71E+09 ph/s/cm2 with 92 equivalent noise photons at
25Hz frame rate, better than the same architecture of InGaAs photodiode array hybridized on an Indigo ROIC ISC9809 with
a pitch of 30 μm for which a readout noise of 120 electrons is observed.
We present several prototypes to extend the range of AlGaN focal plane arrays from near UV to deep UV range
(200 nm - 4 nm). Arrays include 320x256 pixels with a pitch of 30 μm and are based on Schottky photodiodes. AlGaN
is grown on a silicon substrate. After a flip-chip hybridization, silicon substrate is thinned and removed by dry etching.
The tricky point is to maintain the membrane integrity. By using a honeycomb structure in the Si substrate, after
hybridization, we were able to keep the membrane plane and rigid, avoid the crack expansion, and thus maintain the
membrane integrity. The structure includes an Al.35Ga.65N active layer grown on a thick Al.55Ga .45N window layer, with
a graded AlGaN layer in between. The high quality materials are grown by MBE. The Al.55Ga.45N window layer is also
thinned by dry etching down to the gradual layer and desertion layer where a higher internal electric field takes place.
The results show that the dry etching process doesn't affect the readout circuit properties. The dark current is negligible
and non uniformity in etching slightly contributes into a constant offset. The measured noise factor, a bit more than 100
electrons rms, is due to reset noise in the integration capacitance and in other parasitic capacitances. With a peak
response at 300 nm of 35%, the responsivity is 1% at 266 nm and in the deep UV range. The spectral responsivity
measured on a synchrotron line at a wavelength of 2nm reaches more than 200% due to multiple photoexcitation.
Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on GaAs
and related III-V compounds, at the Alcatel-Thales-III-V Lab (formerly part of THALES Research and Technology
Laboratory).
In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key
parameter for the production to start. Another widely claimed advantage for QWIPs was the so-called band-gap
engineering and versatility of the III-V processing allowing the custom design of quantum structures at various
wavelengths in MWIR, LWIR and VLWIR. An overview of the available performances of QWIPs in the whole infrared
spectrum is presented here. We also discuss about the under-development products such as dual band and
polarimetric structures.
Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on
GaAs and related III-V compounds, at the Alcatel-Thales-III-V Lab (formerly part of THALES Research and
Technology Laboratory).
In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key
parameter for the production to start. Another widely claimed advantage for QWIPs was the so-called band-gap
engineering and versatility of the III-V processing allowing the custom design of quantum structures to fulfil the
requirements of specific applications such as very long wavelength (VLWIR) or multispectral detection. In this
presentation, we give the status of our LWIR QWIP production line, and also the current status of QWIPs for MWIR
(<5μm) and VLWIR (>15μm) arrays.
As the QWIP technology cannot cover the full electromagnetic spectrum, we develop other semiconductor
compounds for SWIR and UV applications. We present here the status of our first FPA realization in UV with GaN
alloy, and at 1.5μm with InGaAs photodiodes.
The fast development of nitrides has given the opportunity to investigate AlGaN as a material for ultraviolet detection.
Such camera present an intrinsic spectral selectivity and an extremely low dark current at room temperature. It can
compete with technologies based on photocathodes, MCP intensifiers, back thinned CCD or hybrid CMOS focal plane
arrays (FPA) for low flux measurements. AlGaN based cameras allow UV imaging without filters or with simplified
ones in harsh solar blind conditions. Few results on camera have been shown in the last years, but the ultimate
performances of AlGaN photodiodes couldn't be achieved due to parasitic illumination of multiplexers, responsivity of p
layers in p-i-n structures, or use of cooled readout circuit. Such issues have prevented up to now a large development of
this technology. We present results on focal plane array of 320x256 pixels with a pitch of 30μm for which Schottky
photodiodes are multiplexed with a readout circuit protected by black matrix at room temperature. Theses focal plane
present a peak reponsivity around 280nm and 310nm with a rejection of visible light of four decades only limited by
internal photoemission in contact. Then we will show the capability to outdoor measurements. The noise figure is due to
readout noise of the multiplexer and we will investigate the ultimate capabilities of Schottky diodes or Metal-
Semiconductor-Metal (MSM) technologies to detect extremely low signal. Furthermore, we will consider deep UV
measurements on single pixels MSM from 32nm to 61nm in a front side illumination configuration. Finally, we will
define technology process allowing backside illumination and deep UV imaging.
Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on GaAs and
related III-V compounds, at THALES Research and Technology Laboratory. The QWIP technology allows the
realization of large staring arrays for Thermal Imagers (TI) working in the long-wave infrared (LWIR) band (8-12
μm).
In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key
parameter for the production to start. The 640x512 LWIR focal plane arrays (FPAs) with 20μm pitch was the
demonstration that state of the art performances can be achieved even with small pixels. This opened the field for the
realization of usable and affordable megapixel FPAs. Thales Research & Technology (TRT) has been developing third
generation GaAs LWIR QWIP arrays for volume manufacture of high performance low cost thermal imaging cameras.
In the past, another widely claimed advantage for QWIPs was the so-called band-gap engineering and versatility of the
III-V processing allowing the custom design of quantum structures to fulfil the requirements of specific applications
such as very long wavelength (VLWIR) or multispectral detection. In this presentation, we present the performances of
both our first 384x288, 25 μm pitch, MWIR (3-5μm) / LWIR (8-9 μm) dual-band FPAs, and the current status of
QWIPs for MWIR (< 5μm) and VLWIR (>15μm) arrays.
Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIP) are considered as a technological choice for
3rdgeneration thermal imagers [1], [2].
Since 2001, the THALES Group has been manufacturing sensitive arrays using AsGa based QWIP technology at
THALES Research and Technology Laboratory. This QWIP technology allows the realization of large staring arrays
for Thermal Imagers (TI) working in the Infrared region of the spectrum. The main advantage of this GaAs detector
technology is that it is also used for other commercial devices. The GaAs industry has lead to important improvements
over the last ten years and it reaches now an undeniable level of maturity. As a result the key parameters to reach high
production yield: large substrate and good uniformity characteristics, have already been achieved. Considering
defective pixels, the main usual features are a high operability (> 99.9%) and a low number of clusters having a
maximum of 4 dead pixels.
Another advantage of this III-V technology is the versatility of the design and processing phases. It allows
customizing both the quantum structure and the pixel architecture in order to fulfill the requirements of any specific
applications. The spectral response of QWIPs is intrinsically resonant but the quantum structure can be designed for a
given detection wavelength window ranging from MWIR, LWIR to VLWIR.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.