European consortium explores IR technology for vehicles
Under the auspices of Eurimus (www.eurimus.com)—a European initiative aimed at microsystem development—a number of vendors are currently researching infrared (IR) systems to improve vehicle safety under difficult nighttime and weather conditions. The project aims to develop an IR camera for a car (ICAR) at low cost.
According to the terms of the initiative, Sofradir (Chatenay-Malabry, France; www.sofradir.com) and CEA LETI (Grenoble, France; www-leti.cea.fr) are developing a new IR focal-plane array (IRFPA) for the system, while Umicore IR Glass (Acigne, France; www.optics.umicore.com) is designing a new IR lens based on chalcogenide glass. Engineers at Zeiss Optronic (Oberkochen, Germany; www.zeiss-optronik.de) are building the system's optics and electronics.
Originally, Sofradir developed a 320 × 240-pixel IRFPA with a 45-µm pitch and a fill factor higher than 80% using its amorphous-silicon-based technology. This method yielded a device that was sensitive in the long-wavelength spectral region (7–14 µm) and consumed less than 200 mW at 30°C. According to Sofradir officials, the main advantages of this amorphous-silicon approach are the low thermal time constant that improves image quality and the compatibility of the technology with standard CMOS processes.
To lower the cost of the complete system and yet fulfill the requirements of the driver vision-enhancement system, however, the development team decided to employ an IRFPA with a lower resolution of 160 × 120 pixels with a pitch of 35 µm. For the new device, members of the initiative plan to switch from the standard metallic package.
To further reduce the cost of the final system, members of the ICAR development team abandoned the idea of using traditional germanium (Ge) or zinc selenide (ZnSe) lenses with the detector. Because the process of cutting monocrystalline germanium or ZnSe ingots into blocks and then polishing them to obtain a lens were judged too labor-intensive and costly, researchers turned to Umicore's new chalcogenide glass.
According to Umicore, large-scale production has driven the search for more cost-effective IR optical systems, and IR- transmitting chalcogenide glasses are the ideal candidate for such applications. This type of lens can be molded into finished, spherical, aspherical, and diffractive lenses in medium- to large-scale production runs, eliminating the need for polishing or diamond turning.
To help designers, Umicore teamed up with CEDIP Infrared (Croissy-Beaubourg, France; www.cedip-infrared.com) to demonstrate the difference among dual lens systems built with GeZnSe, germanium, and chalcogenide glasses. The results show that by comparing the modulus of the optical transfer function, the chalcogenide glass is at least as good as the GeZnSe combination. According to members of the ICAR initiative, a specific camera that uses both the 160 × 120-pixel IRFPA sensor and the new lenses from Umicore will result in a prototype camera early this year.