Nanowerk: CMOS devices are normally covered with a silicon nitride coating to protect from moisture and other impurities. The silicon nitride coating limits the range of optical applications because it is impermeable to UV light.
Scientists at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg have found a solution to this problem: "We've developed a new process step," says Werner Brockherde, head of department at Fraunhofer IMS, "that allows us to produce a protective coating with the same properties but which is permeable to blue and UV light."
The trick is to increase the proportion of nitrogen in the coating by fine-tuning the deposition parameters such as pressure and temperature. "This reduces the absorption of shortwave light," explains Brockherde. "This makes CMOS image sensors suitable for use in wavelength ranges down to 200 nanometers," states Brockherde. "With standard passivation the limit was about 450 nanometers."