OLED-on-CMOS integration for optoelectronic sensor applications
Highly-efficient, low-voltage organic light emitting diodes (OLEDs) are well suitable for post-processing integration onto the top metal layer of CMOS devices. This has been proven for OLED microdisplays so far. Moreover, OLEDon-CMOS technology may also be excellently suitable for various optoelectronic sensor applications by combining highly efficient emitters, use of low-cost materials and cost-effective manufacturing together with silicon-inherent photodetectors and CMOS circuitry. The use of OLEDs on CMOS substrates requires a top-emitting, low-voltage and highly efficient OLED structure. By reducing the operating voltage for the OLED below 5V, the costs for the CMOS process can be reduced, because a process without high-voltage option can be used. Red, orange, white, green and blue OLED-stacks with doped charge transport layers were prepared on different dualmetal layer CMOS test substrates without active transistor area. Afterwards, the different devices were measured and compared with respect to their performance (current, luminance, voltage, luminance dependence on viewing angle, optical outcoupling etc.). Low operating voltages of 2.4V at 100cd/m2 for the red p-i-n type phosphorescent emitting OLED stack, 2.5V at 100cd/m2 for the orange phosphorescent emitting OLED stack and 3.2V at 100cd/m2 for the white fluorescent emitting OLED have been achieved here. Therefore, those OLED stacks are suitable for use in a CMOS process even within a regular 5V process option. Moreover, the operating voltage achieved so far is expected to be reduced further when using different top electrode materials. Integrating such OLEDs on a CMOS-substrate provide a preferable choice for silicon-based optical Microsystems targeted towards optoelectronic sensor applications, as there are integrated light barriers, optocouplers, or lab-onchip devices.