American scientists directly integrate VCSEL into electronic chips for use in autonomous driving sensing technology

When you use facial recognition to unlock your phone, how does the phone know it's you? In fact, a set of tiny lasers illuminate your face, and then the phone uses the reflected laser light to build a 3D model, just like a facial topography map. In this way, the phone software can use the model to decide whether to unlock the phone.

This technology is made possible by tiny lasers called vertical-cavity surface-emitting lasers (VCSELs). Traditionally, such lasers have been used for short-range data transmission, laser printers, and even computer mice. However, since they began to appear in mainstream facial recognition and 3D imaging technology, demand for these lasers has exploded, and there has been a demand for such lasers to become more efficient and compact.

According to foreign media reports, Leah Espenhahn, a graduate student in the research group of John Dallesasse, professor of electrical and computer engineering at the UNIVERSITY OF ILLINOIS GRAINGER COLLEGE OF ENGINEERING, demonstrated a method to directly integrate VCSELs into electronic chips. New Technology. She uses a method called epitaxial transfer to create VCSELs directly on silicon microelectronic devices, which is like creating islands for lasers in silicon devices. Compared to standard devices connected to microelectronic devices, VCSELs built using the epitaxial transfer method are more compact, perform better, and are less likely to overheat.”

Espenhahn holds a VCSEL wafer fully integrated on silicon (Image credit: Gregg School of Engineering, University of Illinois at Urbana-Champaign)

VCSEL is a type of semiconductor laser. Like other lasers, it produces an intensely focused beam, but is made entirely of semiconductor materials. This means that the manufacturing technology of electronic microchips, which are also made of semiconductor materials, can be adapted to lasers.

Many semiconductor lasers emit the laser from the side, that is, the beam is parallel to the electrical contacts. Such devices require additional traditional manufacturing steps to ensure a smooth surface for the laser to exit the material smoothly. In contrast, VCSELs generate laser light that is perpendicular to the electrical contacts and passes vertically through the top layer, simplifying the manufacturing process and opening the door to designing more compact devices.

The standard method of creating VCSEL arrays is to manually solder prefabricated lasers to electronic chips in a "flip-chip bonding" manner, a process that is time-consuming and has limited accuracy. If the final device is to be smaller and more efficient, it will need to be integrated directly with the electronics on a microchip.

Espenhahn accomplished this by attaching unprocessed VCSEL device structures to a temporary platform. After etching different "islands" of material for a single laser, a layer of bonding material is placed on top. The temporary platform is then flipped over and placed on top of the main silicon platform, allowing the different "islands" of material to bond together. After the temporary platform is removed, a set of "islands" of material made by the epitaxial transfer method are left, which can be processed into VCSEL devices.

Because VCSELs are fabricated after the transfer process, they can be placed on electronic circuits in a more precise manner than "flip-chip bonded" devices. In addition, the final device will have better thermal performance and greater controllability.

Facial recognition is just one application of lidar technology, which uses reflected laser light to create an image or model on a computer. Another prominent application of VCSEL-based lidar is in autonomous vehicle vision and sensing technology.