Thin‐Film Electrostatic Discharge Protection for Highly Segmented OLEDs in Automotive Applications

Abstract

price reduction of the OLED panels is in focus of today's OLED research [1,3,4] as well as developing further unique selling points and new functionalities for OLEDs in order to preserve the (technology-) lead in future automotive lighting systems. [5] Original equipment manufacturers (OEM) on the other hand claim for display-like lighting solutions capable of acting as communication medium to pedestrians, bike-rider, or the car owner himself before entering the car. Highly segmented OLEDs are a very promising lighting solution: they offer display-like functionality together with precisely distinguishable segment boards and a high quality offstate compared to LED based systems with light guides. [5,6] While automotive lighting requirements regarding luminance and fill factor are fulfilled by highly segmented OLEDs, the intrinsic robustness of OLEDs against electrostatic discharge (ESD) is lost due to the segmentation. An ESD rating of at least 8 kV in the human body-model (HBM) following the JEDEC standard [7] is expected by OEMs. Typically, the HBM ESD testing is performed by connecting the OLED device to a 1.5 kΩ resistance and an external capacitor of typically 200 pF in series. [7] This capacitor is loaded with a voltage of 8 kV before connecting with the OLED device (see Figure S1 in the Supporting Information); e.g., conventional OLED displays built for consumer markets usually offer an ESD rating only up to a level of around 2 kV HBM. [8,9] The higher the capacitance of the OLED device, the lower is the corresponding voltage at the OLED device. Increasing the capacitance of the OLED device, therefore, leads directly to a higher ESD stability of the device (see also Section S1). For example, OLEDs with one large lighting area offer a high capacitance due to the large surface of the OLEDs electrodes, and so a high ESD stability. For highly segmented OLEDs, the total lighting area and its corresponding anode surface is split into many small OLED segments offering only a fraction of capacitance compared to the total OLED lighting area.In this sense, higher ESD stability would require the introduction of external components to protect the small OLED segments, like it is state-of-the-art for single automotive LEDs. However, additional external components would further increase the price of an OLED panel, since each single OLED Future autonomous driving requires new lighting solutions. Communication in between other cars and pedestrians, which fulfills the requirements of the automotive lighting industry, is needed. A very promising lighting solution for this application are highly segmented organic light-emitting diodes (OLEDs). Unfortunately, small area OLEDs are very sensitive to electrostatic discharge due to the small capacitance of the OLED segments. This study presents a solution for highly segmented OLEDs to fulfill automotive requirements regarding electrostatic discharge (ESD) without cost driving external components but through the improvement of the OLED itself. This solution is designed to be cheap a...