Interview with Dr. Martin H. Ettenberg from Princeton Infrared Technologies

  • Dr. Martin H. Ettenberg - President and CEO

GoPhotonics interviewed Dr. Martin H. Ettenberg, the President and CEO of Princeton Infrared Technologies. Martin Ettenberg had been developing InGaAs detectors for over 14 years at Sensors Unlimited Inc./Goodrich Corporation. He joined Sensors Unlimited, Inc. in August of 1997 and began as the principal investigator on two Phase I and two Phase II SBIR programs. Those government programs lead to the development of several camera products that Martin was the product manager and later Director of Imaging Products.

Q. Can you give us a brief history of Princeton Infrared Technologies, Inc.?

Martin Ettenberg: Founded in 2013, Princeton Infrared Technologies, Inc. (PIRT) specialists in indium gallium arsenide (InGaAs) imaging technology, focuses on the design and manufacture of both shortwave infrared (SWIR) cameras, and one- and two-dimensional imaging arrays. With a wide spectral range of sensitivity, 0.4 to 2.1µm, PIRT InGaAs arrays, and cameras are used in machine vision inspection systems as well as bench-top and portable NIR & Raman spectrometers. The SWIR spectral range is also ideal in hyperspectral and multi-spectral imaging systems. PIRT operates a fabless environment with a staff of experienced III-V semiconductor scientists and engineers to provide the highest quality cost-effective detection and imaging expertise for your most exacting applications. This expertise allows for custom SWIR imaging solutions that many other camera manufacturers can’t offer. All of our imaging products are now available with no ITAR export restrictions.

Q. Can you tell us about the Short Wave Infrared (SWIR) imaging and detection technology? What are its advantages over other imaging and detection technologies?

Martin Ettenberg: Shortwave Infrared (SWIR) imaging using lattice-matched InGaAs material provides the highest sensitivity with the lowest noise detection in the SWIR. These materials allow imaging and detection at room temperature without cooling to cryogenic temperatures. PIRT has detectors that image from 0.4 to 1.7 μm using indium gallium arsenide, which are useful for a variety of commercial and defense applications. PIRT also manufactures specialty detectors from 0.4 to 2.1 μm using Type 2 superlattices. Applications include detecting moisture, determining plastic types, as well as imaging lasers. The imagers are excellent for long-range imaging, especially through atmospheric haze, fog, and smoke.

Our cameras “see” things that the human eye can’t see.  Our SWIR cameras “see” beyond the visible wavelength and image reflective and emissive light that is invisible to human eyes. This wavelength band allows thermal imaging of objects hotter than 150°C. The SWIR band can also use glass optics allowing thermal imaging through glass windows. This is something that can’t be done with traditional long-wave or mid-wave infrared thermal imagers. They need expensive sapphire or germanium windows to image. Many objects have different reflective signatures than they do in the visible range allowing for sorting and inspection applications that are difficult in the visible wavelength range. For instance, water is very absorbing so it is easy to detect water or the concentration of water in a material. Imaging in SWIR is very similar to visible imagers, with glass optics, the sun, or LED lights as the source makes using a SWIR system very similar to a visible system.

Q. What are the applications of Short Wave Infrared (SWIR) Technology?

Martin Ettenberg: SWIR imaging is used in commercial, industrialscientific, and defense industries. Industrial applications include agricultural inspection, chemical detection, contaminant detection, moisture detection, semiconductor inspection of Silicon for solar cells and computer chips, and thermal imaging.  Scientific applications include infrared reflectometry in art, astronomy, biological research for cancer markers, and earth monitoring satellites. Defense applications include laser spotting, imaging through smoke, fog, obscurants, and day/night surveillance. These are just a small sampling of SWIR applications.

Q. What is InGaAs? Why do we use InGaAs for SWIR Imaging? What are its advantages over other semiconductor materials?

Martin Ettenberg: InGaAs is short for a specific alloy of 53% Indium Arsenide and 47% Gallium Arsenide (In.53 Ga.47As) which is lattice matched to InP. This means the atomic spacing of the alloys atoms of indium, gallium, and arsenic matches InP. This alloy is grown (manufactured) on InP substrates. Having them lattice matched allows for high sensitivity and low noise material. Lattice matched Indium Gallium Arsenide (InGaAs) is deposited in very thin layers (several atomic layers) at a time on an InP substrate.

This composition of In.53 Ga.47As has an energy gap of 0.74eV which allows the detection of light up to 1.68 µm at 20C. Longer wavelengths of light can be captured with InGaAs alloys with more InAs added to the mixture. When this occurs, one is no longer lattice matched to InP. If the material is not lattice-matched, meaning the atoms don’t line up anymore, then defects occur in the material. These defects produce significant noise in the form of a dark current. The higher dark current makes it harder to detect the small signals as one has to have more light signals to overcome the noise from the excess dark current. PIRT is working with our partners on new material structures like our Type 2 Superlattice to minimize the noise source, known in the industry as dark current (i.e. the noise produced when the material is biased in the dark) at these longer wavelengths. Lower dark current leads to more sensitive devices because there is less noise so one can detect smaller amounts of signal.

Princeton Infrared Technologies, Inc. is utilizing 4” InP substrates, which allow for more chips on a wafer with greater uniformity. These are the largest substrates commercially available. This, in combination with an advanced III-V fabrication partner, enables PIRT to produce InGaAs imagers at a higher quality and at a lower price than the competition as most companies use 3” InP substrates. The state-of-the-art fabrication facility “fab” has cassette-to cassette processing, minimizing human touch with the wafers thus raising yield. In addition to the advanced technology, our partner processes over 1,000 wafers per month of material enabling statistical process control to be deployed. Statistical process control enables the wafer processing to be consistent from run to run thus raising yield and quality. Most infrared fabs don’t run that many InGaAs wafers in a year, let alone a month, limiting their statistical process control and ability to have high yield which is one of the many reasons InGaAs detector arrays are so expensive. PIRT also has the advantage of not running its own fab so there is no large overhead expense passed on to the customer.

PIRT has a unique InGaAs detector structure, which allows for low dark current and the ability to image from 0.4 to 1.7 µm with high Quantum Efficiency. Quantum Efficiency is how effectively the material converts photons detected to electrons that can be measured. This detector structure has demonstrated very low dark currents that are competitive with others in the industry who have been manufacturing for years. This unique detector structure enables a 100% fill factor in our detectors with no dead space between pixels. Astronomers have written about the high quality of our detector material and the low dark current it produces allowing better detection in astronomy applications.

Q. Can you tell us about your product portfolio?

Martin Ettenberg: Princeton Infrared Technologies, Inc. (PIRT) is a fabless semiconductor company specializing in shortwave infrared (SWIR) detector technology and high-performance imaging cameras.  We manufacture both shortwave infrared cameras, and one- and two-dimensional imaging arrays.   Our current product portfolio includes the following: 

  • BPCam - Extended SWIR Camera for Laser Beam Profiling

Extended SWIR response using a Type 2 Superlattice, which is a special InGaAs structure allowing for longer detection to 2.1 µm without defects.  It is placed in our newest camera, the BPCam for laser beam profiling.  The camera supports extended SWIR wavelength response with modest TEC cooled operation.

  • MVCam - SWIR Camera for Machine Vision

The MVCam series SWIR and visible camera supports the highest commercially available frame rate at Megapixel resolution with no ITAR restrictions.

This non-ITAR lattice matched, InGaAs scientific SWIR camera allows for high resolution SWIR imaging at 1280x1024 resolution with a cooled detector allowing very long integration times of >3 minutes.   The larger 12 μm pitch array, combined with the high quantum efficiency of lattice matched InGaAs enables impressive sensitivity in the SWIR and visible spectral bands.

The LineCam12 is an advanced linescan SWIR camera with 14-bit digital data at 37klines/s on USB3 or Camera Link™ outputs. The SWIR camera currently comes in two varieties: 250 μm tall pixels for spectroscopy and 12.5 μm square pixels for machine vision applications.

The 1024L1 is a 1024x1 state of the art InGaAs linear array imager on 12.5 µm pitch that was built for both spectroscopy and machine vision in the shortwave infrared band. The 1024L1-12.5-T is an advanced digital array with the lowest read noise available <110e- for a 250 μm tall pixel.  It is the only linear array in the world capable of both SWIR and visible detection in the same array.

This lattice matched InGaAs 2D SWIR focal plane array (FPA) allows for high resolution SWIR imaging at high frame rates >90fps. This 12 μm pitch array with high resolution combined with the large quantum efficiency of the lattice matched InGaAs arrays enables impressive imaging in the SWIR band.

Q. Can you tell us more about the BPCam Product? What are some applications where it can be used?

Martin Ettenberg: The 1280BPCam is designed to provide a new inspection and characterization alternative to manufacturers of lasers, light sources, and optical components in the extended shortwave infrared (eSWIR) spectrum beyond the lattice-matched InGaAs wavelength cutoff of 1.7 µm. The camera has sensitivity from 400 to 2100 nm at a high resolution of 1280 x 1024 pixels on a 12 µm pitch using a newer Type 2 Superlattice technology. The BPCam is quite unique offering such a wide spectral response at such a high QE with high resolution. Existing camera sensor technologies, InSb and MCT, must be cryogenically cooled, requiring periodic maintenance or cooler replacement. While newer colloidal quantum dot technology offers longer wavelength detection but with very poor quantum efficiency. Extended InGaAs have been available for years, but most are lower resolution and the imaging quality is poor due to the need to image through the defects in the material from the lattice mismatched material.

To profile lasers at longer wavelengths in the past required moving a single-element diode to scan the laser or to use one of these expensive cryogenic cameras. So-called extended InGaAs exhibits higher noise and is not generally available in area imaging camera because of poor image quality due to imaging through defects in the material. This makes beam profiling difficult. To get extended InGaAs material also requires a short turn on wavelength of 1.2um limiting their use in the near-infrared and visible region. The Type 2 Superlattice (T2SL) imager developed by PIRT for this 1280BPCam yields better performance (lower noise and higher quantum efficiency) at a better price point with less cooling than technologies with equivalent capabilities. It is lattice-matched material so for beam profiling there is no issue with imaging through defects like in extended InGaAs detectors. This combined with its fast frame rate of 90 frames per second at full resolution with a 14-bit dynamic range makes it a flexible imaging instrument.

Prior to this, imaging spectroscopy was also difficult as one had to scan a single-element device in two dimensions at different wavelengths. This took a significant amount of time and a complicated scanning system. An area array allows for much simpler hyperspectral imaging as one needs to either scan in one direction or simply change wavelengths from frame to frame. This allows for a much simpler and faster system. Inspection can now be conducted in real-time.

Princeton Infrared Technologies, Inc. (PIRT) is a fabless semiconductor company specializing in shortwave infrared (SWIR) detector technology and high-performance imaging cameras. Our 1280BPCam is just the latest innovation to enable laser beam profiling and spectral imaging beyond traditional 1.7 µm InGaAs. Our unique Type 2 Superlattice, T2SL, image sensor incorporated in BPCam allows for a whole new suite of SWIR detection products out to 2100 nm. This material was developed through an Air Force SBIR program and PIRT leveraged this material development to build a commercial product which is now being deployed in commercial instances and on a Navy program.

Q. Do you offer Custom Foundry Services? What type of custom products can you develop?

Martin Ettenberg: Yes, we do offer custom foundry services. We develop custom detector types as well as imager and cameras for different applications.  Our knowledge of InGaAs detector arrays is unparalleled in the industry. We work with various engineering teams on the specifications needed for their SWIR applications. PIRT has customized cameras and imaging arrays by working with various partner organizations to get the imaging array needed.

Q. Can you tell us about your SWIR testing lab and other research facilities? Where are they located?

Martin Ettenberg: Our SWIR Testing Lab was created to help find the best SWIR imaging solutions for various imaging challenges.  The lab was created because we are always being asked “Do you think you can image my issue in the SWIR?”  We won’t know until we look at it with our cameras under various lighting conditions which was the genesis for our SWIR testing lab. We wanted to see if a SWIR imager could solve our customer’s imaging issue. Many variables can impact whether SWIR imaging will detect what is needed for a specific application. Our applications group created this testing lab, located in Monmouth Junction, NJ, to assist potential customers with their imaging needs. We ask that potential customers send us samples of items they are trying to image, along with imaging challenges they are facing, and we test the items with our SWIR cameras. Our SWIR Applications Lab has LED light sources, bandpass filters across several visible and SWIR bands of interest, polarization filters, as well as a test conveyor belt for emulating typical linescan camera applications. Our SWIR cameras feature high sensitivity, high-dynamic range, and great linearity across the wide wavelength range of 0.4 to 2.1 μm, ensuring the performance needed to record small variations in materials. With both area (2-D) and line (1-D) cameras and adjustable light sources, PIRT can test several imaging scenarios to find the best solution.

Q. Who are your customers? Where are they located (can you give us a % breakup by continent)?

Martin Ettenberg: We are proud to say that we sell our SWIR cameras and imagers domestically and internationally. We have a broad customer base including universities, observatories, government agencies, industrial, commercial, and manufacturing companies. We sell about 40% of our cameras in the U.S. and 30% in Europe and 30% in Asia.

Q. What is your product and technology roadmap for the next three years?

Martin Ettenberg: PIRT has two areas of focus for the next three years:

The first is to lower the cost of imagers by pushing a smaller pitch. We are also leveraging manufacturing technologies from the Si industry. We are pushing wafer-scale hybridization to drive down costs. Today imagers are manufactured one at a time, but we are developing methods to hybridize the entire InGaAs wafer at once which will significantly reduce costs while allowing for smaller pitch and larger area format arrays.

The second area is longer wavelength detection. The eventual goal is a detector that covers from 400nm to 2600nm with minimal cooling and high quantum efficiency. This type of wide waveband detector will enable a host of new applications and detection of phenomenology that is currently invisible to our eyes.

Princeton Infrared Technologies is also exploring very high-resolution arrays for various applications. This would be funded research that could lead to a commercial product.

About Princeton Infrared Technologies

Princeton Infrared Technologies is a fabless infrared company focused on the design, test, and final assembly of infrared imaging and detection products specializing in InGaAs detector arrays. These detector materials are used to detect light beyond what our eyes see in the Near Infrared as well as Short Wave Infrared (900 nm-1700 nm) versus visible light (400-750 nm). Detectors and cameras are similar to cell phone cameras except they see infrared light that our human eyes do not see. There are numerous applications for imaging and detecting light beyond what humans can image with our eyes including applications that need to detect moisture, temperature, or specific laser wavelengths, i.e. laser designators for dropping bombs and eye-safe lasers used in range finders.

Click here to visit Princeton Infrared Technologies' Profile on Gophotonics.