Digital 640x512 / 15μm InSb detector for high frame rate, high
sensitivity and low power applications
T. Markovitz, I. Pivnik, Z. Calahorra, E. Ilan, I. Hirsh, E. Zeierman, M. Eylon, E. Kahanov,
I. Kogan, N. Fishler, M. Brumer and I. Lukomsky
SemiConductor Devices P.O. Box 2250, Haifa 31021, Israel
ABSTRACT
Pelican-D is a new digital 640x512 / 15μm InSb detector developed by SCD to serve a number of applications. The
Readout Integrated Circuit (ROIC) has a digital output which can be calibrated to a signal resolution in the 13-15 bit
range. Besides the digital output, the detector has some additional advantages over other MWIR detectors of the same
format. The high frequency of data output, which supports a full image frame rate of over 300Hz, is very useful in
systems that track fast evolving events such as Missile Warning Systems (MWS), Missile Seekers and some
Thermographic applications. Another important characteristic of the detector is related to an operation mode with
relatively low readout noise. This mode of operation is especially beneficial in applications where the background
radiation is low such as in long range surveillance systems. For imaging systems where very high sensitivity is required,
the ROIC can be coupled to an epi-InSb detector array and have a dark current at 77K that is lower by a factor of 15 with
respect to standard InSb. Alternatively, Pelican-D with epi-InSb can be operated at 95K with a standard dark current and
sensitivity. Such an elevated operating temperature enables the use of cryogenic coolers of relatively low size, weight
and power for applications such as Hand-held cameras, miniature gimbaled systems, and light UAVs. In this work we
present in detail the characteristic performance of the new detector and its applications.
Keywords: Infrared Detector, InSb, Focal Plane Array, High Frame Rate, Low Power, Pelican-D
1. INTRODUCTION
A recent trend in the development of large format IR detectors is a shift towards smaller pixel size. This is in order to
reduce the overall size of the Focal Plane Array (FPA) in a specific format. Naturally, the reduction in FPA size yields a
decrease in the overall Size, Weight and Power consumption (SWaP) of the integrated detector. Alternatively, one can
maintain the array size and increase the number of pixels while keeping a high image quality and high frame rate while
the number of pixels in the array is substantially increased. We have introduced two families of detectors in former
publications that are part of this development trend. The first is Pelican[1], which has a 640x512 format and a 15μm pitch.
The second is Hercules[1][2] which has a 1280x1024 format, also with a 15μm pitch. In this article we present a new
family of detectors that is based on a novel ROIC named Digital Pelican (Pelican-D). The Pelican-D ROIC has the same
format and pitch as the analog Pelican. However, it enjoys the advantages of a digital ROIC and includes some unique
features such as a high sensitivity mode and a high frame rate. In the following sections we discuss in detail the PelicanD ROIC and FPA and present their performance parameters. In the last section, we show different configurations of the
integrated detector. These were developed in order to meet a large variety of applications, from compact ones like
handheld goggles, and up to high-end applications such as Missile Seeker or Missile Warning Systems (MWS)[3].
2. PELICAN-D ROIC AND FPA
2.1 Pelican-D ROIC
Since 2002 SCD has been developing and producing ROICs with analog to digital conversion at the focal plane, known
as the Sebastian family of ROICs[4]. Three formats of Sebastian ROICs were developed: 320×256, 480×384 and
640×512, all with a 20μm pixel size and all based on a 0.5μm CMOS process[5]. Sebastian combines a high level of
functionality with special operation modes and excellent performance, especially high linearity and low Residual Non
Uniformity (RNU). The Sebastian family is the basis for our new line of digital ROICs with a 15μm pitch. The first
member of this new series, named Hercules, is a mega-pixel format and is described elsewhere[2]. The second member is
the Pelican-D which has the same format as the analog Pelican[1], namely 640x512 elements. The main challenge in the
design of a 15μm pixel has been to maintain the performance level and functionality of Sebastian in half a pixel area.
These constraints require the use of a more advanced CMOS process. Therefore we chose a 0.18μm fabrication process.
A smaller pixel size and a larger format array can affect the following parameters of the ROIC: Integration capacitance,
Power consumption, Pixel readout rate, Functionality, and Readout noise. The migration to the 0.18μm CMOS process
has enabled these parameters to be addressed, as this process offers the following advantages:
• Higher value of capacitance per unit area which partially compensates for the small pixel area
• Lower operating voltage which reduces power consumption
• High speed digital circuits
• Denser layout of devices, which enables a high level of functionality
• Use of a dual threshold voltage (Vth) process, which enables operation of the analog circuits at a high voltage and the
digital circuits at a low voltage
The PelicanD ROIC design is based on the Hercules design with the necessary adaptations required for the smaller
format. As such, it has versatile modes of operation to support different types of application. The ROIC is designed to
operate at a clock rate of 80MHz, where the pixel readout rate from the ROIC to the proximity electronics is up to
160MHz. This results in a maximum frame rate of over 300Hz at full window size. The ability to operate at such high
frame rate can be used by systems that track fast moving objects such as MWS and Missile Seekers[3] or by applications
that require sampling of a large amount of data in a short time, such as Thermographic applications or testers for non
destructive measurements. The ROIC power consumption in this high speed mode is about 75mW. This value is
relatively low and is not considered to be a challenge for standard 1/2 Watt cryo-coolers.
For handheld applications, the power consumption of the overall product is a critical parameter. For this type of
application, the power consumption of the ROIC can be even lower. The measured power consumption of the ROIC
while configured to low power operation at a 60Hz frame rate is below 50mW. This value is similar to that achieved with
analog ROICs sharing the same format (such as analog Pelican[1]) although they do not include signal digitization
circuits on the focal plane. This is due to the carful design of the Pelican-D ROIC and the benefits of its fabrication
process discussed above.
The pixel design uses voltage readout where the integration capacitance is 5.8Me- for Integration Then Read (ITR) and
Integration While Read (IWR) operation modes. An in-pixel gain was implemented in order to reduce readout noise,
which is otherwise dominant in the readout channel. The use of the higher gain mode can improve the Signal to Noise
Ratio (SNR) in scenarios where the photon flux is very low. This mode is beneficial for applications having high F/# or
those that are staring at cold scenes.
2.2 Pelican-D FPA
The Pelican-D FPA uses an InSb array of photo-diodes that is flip-chip bonded to the Pelican-D ROIC. Two types of
Pelican-D FPAs are available. The first configuration is with an InSb array that is manufactured using SCD's planar
fabrication technology (Standard Pelican-D FPA). This technology is well established at SCD and exhibits high
uniformity and high operability. The planar technology was first adapted to a 15 μm pixel in 2006 as part of the
development of the analog Pelican[1]. Since then, thousands of FPA's have been manufactured, assembled into detectors
and successfully integrated into systems. The second configuration of Pelican-D FPA is with an InSb array that is
manufactured using an epitaxial growth technique (Epi Pelican-D FPA). In this technique, the InSb p-n diode is grown
by Molecular Beam Epitaxy (MBE) and the pixels are defined by mesa etch[6]. Such high control of the material during
the diode production lowers the defect density inside the epi-InSb diode in comparison to the standard planar method
where the p-n junction is formed by ion implantation. Therefore, the dark current of the device is reduced by an order of
magnitude. The low dark current enables a new line of detectors that are operated at an elevated temperature (95K) while
keeping the same high image quality as in the standard detectors which are operated at 80K. Hence, an Epi Pelican-D
detector can be cooled with a smaller cooler, having lower SWaP (see details in section 4.2). These are critical
parameters for applications such as hand-held cameras and miniature gimbaled systems. The typical performance
parameters of different Pelican-D detector configurations are detailed in the following sections.
3. RADIOMETRIC PERFORMANCE OF PELICAN-D FPA
Pelican-D detectors share the same high quality image as Pelican[1]. In the following sections we present measurements
of key performance parameters for the Pelican-D detector.
3.1 Detector sensitivity - Noise and NETD
The noise of a detector and its responsivity defines the limit of sensitivity for an IR system. The following graph shows
the square of the total noise measured as a function of the signal in a Pelican-D detector. The pixel signal is defined as
mean value averaged over 64 consecutive frames, while its noise is the standard deviation of this sequence of frames.
The detector is facing an extended blackbody at 25°C and the signal is varied by changing the integration time.
6
x 10
6
Noise2 [No. of e- 2]
5
4
3
2
1
0
0
10
20
30
40
50
60
Well Fill Capacity [%]
70
80
90
Figure 1 – The measured square of the total noise of the detector as a function of its signal
As expected, the graph shows a linear dependence which means that the noise of the detector is a pure combination of
the detector readout noise (noise at zero well fill capacity) and the shot noise originating from the photo diode current
that is integrated in the detector capacitor. This specific measurement was performed with a standard Pelican-D detector
operated using the 5.8Me- integration capacitor. In this operation mode, the noise floor of the detector is about 900e-.
One should note that the total noise of the detector is also the total noise of the system, since Pelican-D has an analog to
digital converters at the focal plane.
The sensitivity of a 2-D MWIR array is traditionally defined by its Noise Equivalent Temperature Difference (NETD),
which is the ratio between the measured noise and the measured responsivity of the detector. Figure 2 shows a histogram
of the measured NETD of a Pelican-D detector. The measurement was performed using an F/4 configuration, with an
integration time of about 9ms, while facing a uniform blackbody at 20°C. The resulting well fill in this case is 50% of a
maximum of 5.8Me-. As can be seen, the NETD distribution is quite narrow having an average NETD value of about
20mK. An image of the NETD measurement is presented in Figure 3. It shows a random spatial distribution of the
NETD with no specific spatial patterns.
6000
5000
No. of Pixels
4000
3000
2000
1000
0
5
10
15
20
NETD [mK]
25
30
35
Figure 2 – NETD histogram of typical Pelican-D detector.
23 mK
50
22
100
21
150
200
20
250
19
300
18
350
17
400
16
450
500
100
200
300
400
Figure 3 –The distribution of the NETD values across the Pelican-D array
500
600
15
3.2 Detector image uniformity
The uniformity of a detector affects the ability of a staring system to distinguish between elements in the IR image. The
image uniformity of a detector is defined by the RNU of the image after performing a two point Non Uniformity
Correction (NUC). Figure 4 shows an RNU measurement of a Pelican-D detector that was operated using a 5.8Meintegration capacitor. Here the integration time was fixed to 3ms while the temperature of an extended blackbody was
varied in the range of 13°C to 78°C. This yield a span of signals from 10% to 80% well fills. In order to perform a NUC
we used signal measurements at 17% and 80% well fill and applied 2-point linear correction. The RNU is calculated as
the ratio between the standard deviation (STD) of the corrected image divided by the total range of the signal. The
measured RNU of Pelican-D is found to be below 0.02% STD/full span for a large span of signals (set 1 in Figure 4).
This RNU value represents a high quality corrected image, similar to the measured performance of a typical analog
Pelican[1].
0.08
Residual Non Uniformity [% from full span]
First Mesurement
Second Mesurement
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
10
20
30
40
50
W ell Fill Capacity[%]
60
70
80
Figure 4 – RNU as a function of well-fill capacity. The crosses show the RNU of a measurement done immediately after the
cool-down of the detector (set-1). The open circles represent the RNU of a second set of measurements (set-2) performed 4
hours after the cooldown and corrected using the correction coefficients of set-1.
The high stability of the RNU as a function of time is also demonstrated in Figure 4. In this experiment, we re-measured
the detector signals after 4 hours of continuous operation. This new set of measurements (set-2) was corrected using the
correction coefficients of the original set of measurements (set-1) that were recorded immediately after the cool down of
the detector. As can be seen, the two sets of RNU values fall one on top of the other, demonstrating the high stability of
the detector's corrected image.
3.3 Image quality – Spatial Resolution and Operability
The image quality of an IR detector depends on the above mentioned parameters, namely the RNU and the NETD.
However, two more important parameters affect the quality of the image. The first one is the image spatial resolution.
This depends on the pixel Modulation Transfer Function (MTF). The improved MTF for a 15µm InSb pixel has already
been shown[1]. The second parameter is the percentage of operable pixels. A typical operability of Pelican-D is about
99.9%. This is tested by applying standard criteria for defective elements, such as NETD defects, spatial non uniformity
defects, etc.
3.4 High speed operation
A unique characteristic of the Pelican-D detector is its ability to operate with a frame rate as high as 300Hz for a full
640x512 image. This is achieved without degrading of the radiometric performance. As an example, in Figure 5 we
compare the RNU measured at 60Hz and at 300Hz. As can be seen, the results are identical.
0.05
300Hz
60Hz
Residual Non Uniformity [% from full span]
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
10
20
30
40
50
60
W ell Fill Capacity[%]
70
80
90
Figure 5 – RNU of PelicanD: Comparison between operations at 60Hz and at 300Hz.
High speed operation not only means the ability to run at high frame rate, but also a fast response of the ROIC to a
change in the mode of operation. Applications that process image information in real time require that a change of
operation mode shall be on a frame to frame basis. The following operation parameters can be changed in Pelican-D in
such manner via serial communication:
•
Integration time
•
Integration mode (ITR/IWR)
•
Readout mode (Standard/Dilution)
•
Gain
•
Windowing
•
Frame rate
•
A/D conversion resolution
In the following figure, we present a real time analysis of the detector signal, while changing the integration time. Here
the detector is operated with an integration time of 5.2ms which results in an average image signal of about 5492 Digital
Levels (DL). During this test, a sequence of consecutive frames was recorded and at a specific pre-defined point in time
(frame # 40) a command for a shorter integration time (Tint = 2.6ms) was sent to the detector. By analyzing the signal
level we see that the command was accepted during frame # 40 and executed during frame # 41.
5497
Mean Signal [DL]
5492
5487
3070
3065
20
25
30
35
40
Frame No.
45
50
55
60
Figure 6 – Change of integration time on a frame to frame basis.
We observe similar behavior for the remaining command parameters that are on the above list. For most of the mode
transitions, a perfect performance is achieved immediately at the first frame after the operation mode change. However,
for part of the transitions there is some residual effect in the first frame. This residual effect in the image completely
disappears in the second frame after the mode transition.
4. PELICAN-D DDCE CONFIGURATIONS
The Pelican-D FPA was developed to fit into all standard Pelican configurations. Hence, the Pelican-D detector uses the
same Dewars, coolers, cold shields and optics that have already been developed for the analog Pelican[1]. Therefore, the
time to market for a new configuration of Pelican-D is relatively short, since we can use off-the-shelf components which
are already qualified.
A component that was developed specifically for the Pelican-D detector is its proximity electronics. The main concept of
this electrical interface is to enable simple integration of the detector to the system. Hence, the proximity electronics
require only one, 5V, power supply. It also includes an FPGA that acts as a mediator between the system and the digital
ROIC. The FPGA transmits the digital output in a camera-link format to the system and synchronizes the detector
operation to an F-sync signal received from the system. In addition, the electrical ICD of the Pelican-D detector
electronics is identical to that of Sebastian480 and is very similar to all other SCD digital detectors[1],[7]. Therefore,
interfacing with Pelican-D is simple and straight forward.
In the following section, we discuss in detail two basic configurations of Pelican-D. One, which is the most commonly
used, is the 'multipurpose' configuration. The second configuration is 'mini Pelican-D' that was developed specifically for
applications that require low SWaP. Two more configurations exist that are not discussed here. These are the 'airborne'
configuration that is optimized for high vibration environments and the 'Piccolo Pelican-D' that is optimized for handheld
applications. These configurations are similar to those of the analog Pelican, and have been described previously[1].
4.1 Multipurpose Pelican-D
A multipurpose Pelican-D is a product that is designed to meet most of the common requirements from an IR detector.
This is in terms of physical dimensions, environmental conditions and radiometric performance.
The multipurpose Pelican-D may be used in ground mobile applications such as IRST systems, targeting systems,
thermography cameras and even some of the airborne applications. An image of the detector is shown in Figure 7.
Figure 7 – An image of a multipurpose Pelican-D detector
The typical parameters of the multipurpose Pelican-D detector are summarized in the following table.
Table 1. The multipurpose Pelican-D typical parameters
Parameter
Typical value
FPA
Planar InSb Pelican-D operated at 80K
Spectral bend
1-5.4μm (cold filter dependent)
Cooling engines
Rotary Integral: Ricor K508 / K508N
Split: Ricor K549, Thales LSF 9997
Weight
600 gr (with K508)
Size (optical axis)
140 mm (with K508)
Frame rate
Up to 300Hz
Cooler power consumption
at steady state @ 23°C
6W (with K508)
Cool-down time @ 23°C
5 minutes (with K508)
Residual Non Uniformity
0.03% STD/Full span
NETD with F/4 and 50%
well-fill
20 mK
Operability
> 99.5%
4.2 Mini Pelican-D
The mini Pelican-D configuration is a detector that is optimized for low SWaP. Hence, it is optimal for use in various
handheld applications or in miniature gimbaled systems. In order to achieve lower SWaP parameters, we use the epi InSb
Pelican-D FPA that is operated at 95K[6]. The ability to operate the InSb detector at this temperature with the same
performance as for a planar InSb detector at 80K allows the use of a compact cooler such as Ricor K562S. This results in
a configuration that has shorter length and lighter weight. In addition, the Dewar for this configuration is optimized for a
lower heat load and therefore the cooler power consumption is further reduced. An image of the detector is shown in
Figure 8, and its typical parameters are given in Table 2.
Figure 8 – An image of the Mini Pelican-D Detector
Table 2. The mini Pelican-D typical parameters
Parameter
Typical value
FPA
Epi InSb Pelican-D operated at 95K
Spectral bend
3.4-5.4μm (cold filter dependent)
Cooling engines
Rotary Integral: Ricor K562S
Weight
300 gr
Size (optical axis)
98 mm (cold stop to FPA distance
14.5mm)
Frame rate
60Hz
Cooler power consumption
at steady state @ 23°C
3.5W
Cool-down time @ 23°C
5 minutes
Residual Non Uniformity
0.03% STD/Full span
NETD with F/4 and 50%
well-fill
20 mK
Operability
> 99.5%
5. SUMMARY
In this article we have presented a new SCD product: the Pelican-D InSb detector. It has a 640x512 format and a 15μm
pitch array. The ROIC has a digital output with the ability to operate at frame rates as high as 300Hz. The Pelican-D
FPA radiometric characteristics were presented. They show high sensitivity, uniformity, spatial resolution and
operability, all of which lead to a high image quality. The FPA can be assembled in different mechanical configurations
in order to support a large variety of applications such as Surveillance, Handheld Goggles, Airborne MWS, Remote
Weapon Stations, Non-Destructive Testing and UAV’s.
Acknowledgments: We would like to thank the SCD personnel who were involved in the development of the Pelican-D
detector. Specifically, Willie Freiman and Yaakov Milstain for their part in the development of the Pelican-D ROIC,
Rahel Elishkov, Emanuel Mordechai and Lior Shkedy for their contribution to the detector testing, and Igal Kogan,
Arkady Marhasev and Amit Serebrenikov for their part in the development of the detector electronics. In addition, we
would like to thank Victor Srur for his support in the assembly of the first Pelican-D detectors, Amir Eisenberg for his
work in transferring the project to production, and Tatyana Scwiertz for assuring the quality of the project.
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