Mapping Temperature in OLED Displays Using CCD Thermoreflectance

Abstract

Effective thermal management is essential to engineering organic devices, since heating accelerates their degradation. However, as pixels in organic light-emitting diode (OLED) displays continue to shrink, an important tool for thermal management, infrared thermography, approaches the limits of its spatial resolution. To address this problem, we adapt highresolution thermoreflectance imaging, which measures minute changes in reflectivity of visible light, to map temperature in a commercial OLED display. We identify a slowly varying thermal signal and find strong evidence of thermal crosstalk, in which a biased pixel heats up its nearest neighbors, even when the neighbors are unbiased. Such crosstalk is indicative of insufficient heat dissipation, which can lead to reduced display lifetime.Index Terms-Thermal management of electronics, photothermal effects, organic light emitting diodes, displays.

LED Junction Temperature Measurement: From Steady State to Transient State

“…By generating thermal images, it can display the temperature curve of organic light-emitting diodes (OLEDs) over time, and the thermal crosstalk of adjacent pixels can be observed. The experimental setup is illustrated in Figure 13, utilizing an inorganic LED as the light source for the optical microscope, reflected from the OLED display, and imaged by the CCD camera [104]. Kendig et al [105] used thermal reflection imaging to determine the two-dimensional temperature pattern of encapsulated UV and blue LEDs.…”

“…Katz et al [104] quantified changes in reflectivity normalization concerning commercial OLED displays, albeit with a limitation in resolution. While a time resolution of approximately milliseconds can be achieved in the measurement of junction temperature, it is essential to acknowledge the low resolution inherent in this approach.…”

“…To address these challenges, the relative timing of the camera, LED, and pixel operations should be meticulously selected, as demonstrated in the experiment depicted in Figure 14. Katz et al [104] quantified changes in reflectivity normalization concerning commercial OLED displays, albeit with a limitation in resolution. While a time resolution of approximately milliseconds can be achieved in the measurement of junction temperature, it is essential to acknowledge the low resolution inherent in this approach.…”

“…The time resolution is contingent upon the minimum pulse width. To capture multi-cycle image signals, a longer CCD exposure time is configured, resulting in a substantial enhancement in the signal-tonoise ratio [100][101][102][103][104][105][106][107][108][109][110]. Figure 18b demonstrates the setting of the sampling pulse signal during the cooling process according to the Boxcar principle.…”