P‐171: A Novel Sensor for Simultaneously Monitoring the Composition and Thickness of Co‐deposited Films During Co‐deposition

Abstract

Organic light emitting diodes are extremely sensitive to dopant concentrations in emitting layers. We developed a sensor that could simultaneously monitor the composition and thickness of co-deposited films. This sensor enables more precise control of the composition of the emitting layers compared to quartz crystal oscillator thickness monitors. IntroductionEmitting layers for organic light emitting diodes (OLEDs) are generally composed of codeposited films of dopant and host molecules. The performance of OLEDs is strongly influenced by the concentrations of dopants in the emitting layers ( Fig. 1). Thus, precise control of the concentrations of dopants is important to obtain uniform performance of OLED devices fabricated at different times. In general, the composition of the dopant and host are controlled by quartz crystal oscillator thickness monitors (QCMs). QCMs can monitor the thickness of only one material. Since both host and dopant molecules adhere to substrates from source heaters during co-deposition, direct monitoring of the composition of the host and dopant near the sample substrate cannot be performed by QCM. This gives rise to the following two problems. (1) Recently, some types of vacuum deposition systems for mass production have been developed. In the case of some types of such new deposition systems, including planer source systems [1] and hot-wall chamber systems [2], vapors of the host and dopant exist throughout the deposition chamber. Thus, the composition of the emitting layers near the sample substrate cannot be monitored by QCM.Thus, precisely monitoring the composition of the host and dopant is difficult in the case of such new deposition systems for mass production. (2) In the case of conventional co-deposition, two QCMs placed near the sources of each material are used to monitor the deposition rate of both materials (Fig. 2). This method cannot precisely monitor the composition of both materials on the sample substrate because the monitored deposition rate is slightly different from the actual rate on the sample substrate. This difference is due to the changes in the material quantities in the furnaces.These two problems can be solved with a sensor that can simultaneously monitor the composition and thickness of an emitting layer. In this paper, we present a novel type of sensor that can monitor the composition and thickness of an emitting layer using only one sensor head. Monitoring MethodFigure 3 shows a schematic of the methods for monitoring the composition and thickness of codeposited films. Codeposited films of host and dopant molecules were deposited on the surfaces of two prisms. Irradiated laser light with wavelengths of 405 and 440 nm was absorbed by the codeposited films. We monitored the absorption of the light during codeposition and calculated the thickness and composition of the codeposited films from the absorption of the irradiated laser light. Host Vacuum chamber Sample substrate QCM Dopant QCM Host Vacuum chamber Sample substrate QCM Dopant QCM Figure 1. Luminesce...