Telescope Releases Pixel-Packed IR Image

The first infrared image obtained using a new sensor on the University of Hawaii’s 88-in. telescope was released. This capability provides a significant step forward in astronomical infrared technology.

The University of Hawaii’s 16-megapixel HAWAII (HgCdTe Astronomical Wide Area Infrared Imager) H4RG-15 sensor is the culmination of a 20-year, $15 million effort that has developed five generations of increasingly larger and more powerful infrared sensors. The detector boasts 16 times the pixel count of an earlier one developed by the same team and installed on the Hubble Space Telescope during the astronauts’ last refurbishment mission. It also has four times the pixel count of the largest infrared sensors now in use at telescopes around the world.

On Thursday, the institute released the first image taken using the new sensor — a picture of the Whirlpool Galaxy, 23 million light-years away.

The field observed is 4096 pixels square and half the diameter of the moon. It is centered on the Whirlpool Galaxy (M51) in the constellation Canes Venatici, which is seen face-on. It is gravitationally interacting with the smaller companion galaxy. Spectacular star formation was triggered by this companion coming through the main disk of M51 about 500 million years ago and looping back through it in the last 50 to 100 million years. M51 can be seen through binoculars at a dark-sky site and is familiar to amateur astronomers. (Image: UH Institute for Astronomy)

“The detail captured all across this extended infrared image really whets our appetite for getting these sensors into cameras at newer, much larger telescopes,” said Donald Hall of the UH Institute for Astronomy, who is principal investigator for the project. “The level of detail revealed by digitally zooming in anywhere in the 16-megapixel image is truly incredible.”

Although the 16-megapixel count is comparable to commercial imagers in current professional digital cameras, infrared sensors for astronomy applications must overcome two technical challenges: The pixels must be sensitive to infrared colors, and they must be large enough to match the huge magnification of the image from a big telescope.

Front and back views of a 2-1/2-in.-sq H4RG-15 sensor mounted to its silicon carbide package. Teledyne Imaging Sensors, a world leader in creating infrared sensors, electrically connects infrared-sensitive crystals to each of the 16 million pixels by growing an alloy of mercury telluride and cadmium telluride onto a wafer that matches the readout, implanting the 16 million individual photodiodes and depositing a tiny (0.0002 in.) dot of indium at the center of each pixel. This infrared detector array is then precisely aligned with matching indium dots on the CMOS readout, and the two are clamped together with hundreds of pounds of force to complete the electrical connections, a process known as hybridization. Teledyne then mounts the hybrid sensor to a custom package produced by GL Scientific. (Image: GL Scientific)

The university’s H4RG-15 overcame these obstacles through an academic-industrial partnership between the institute, Teledyne Scientific and Imaging, GL Scientific and ON Semiconductor.

To overcome the first challenge, the team developed infrared-sensitive crystals that were electrically connected to each of the 16 million pixels.

The second challenge was matching the image scale at the focus of a large telescope, which resulted in the creation of one of the largest silicon chips ever made.

The four H4RG-15 readouts that can be fitted onto an 8-in. silicon wafer (shown left) contrast to the 400-plus typical computer chips in the wafer at right. (For comparison, an iPhone camera chip will easily fit within the pen.) The unprecedented yields for these very large scale silicon readouts can be attributed to the expertise and yield improvement efforts made by ON Semiconductor’s wafer fabrication teams driven by the Custom Foundry Business Unit. The achievement is a direct result of the company’s more than 35-year focus on meeting the technical needs of their military and aeronautics customers. The silicon wafers for these H4RG-15 readouts were manufactured at ON Semiconductor’s wafer manufacturing facility located in Gresham, Ore. (Image: ON Semiconductor)

The ability to construct larger sensors by assembling mosaics of individual arrays could yield 64-megapixel and even gigapixel-class infrared sensors.

“These detectors are vital to the long-term success of the James Webb Space Telescope and other upcoming space astronomy missions,” Hall said. “They also greatly improve the infrared sensitivity of ground-based telescopes such as those on Mauna Kea today and are critical for the coming generation of 30-m-class telescopes, including the Thirty Meter Telescope planned for Mauna Kea.”

For more information, visit: www.ifa.hawaii.edu