Patterning Micron-Sized Features of Quantum Dots and Metal Electrodes

In QD-LEDs, quantum dots can be patterned by spincasting a monolayer onto a relief poly(dimethylsiloxane) (PDMS) stamp and then transferring the pattern onto an organic substrate [1]. However, the spin-cast process requires significant use of material. An alternative solution is to directly pattern the dots using thermal inkjet pico-fluidic drop dispensing system (TIPS) provided by Hewlett-Packard (Figure 1a). A process for formation of patterned monolayer using this technique is currently being developed. Patterning of electrodes in OLED or QD-LED displays presently is done primarily by shadow masking, which is limited in resolution; or cold-welding, which requires high pressures, additional protection layers, use of gold electrode, or subsequent dry etching steps [2-3]. Recently transfer printing has been demonstrated with PDMS on various materials [4]. We are investigating subtractive pattering of silver or silver-magnesium electrodes with untreated PDMS stamp. We demonstrated 25 micron-sized features with good yield on 20 nm thick silver-magnesium films (Figure 1b). This PDMS lift-off technique applied on an OLED electrode made of 50 nm silver film on top of 50 nm silvermagnesium yields OLEDs with the same quantum efficiency and current voltage characteristics to OLEDs defined by shadow masking (Figure 2).