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OLED THRESHOLD VOLTAGE CONTROL

IP.com Disclosure Number: IPCOM000015457D
Original Publication Date: 2001-Dec-23
Included in the Prior Art Database: 2003-Jun-20
Document File: 3 page(s) / 87K

Publishing Venue

IBM

Abstract

It is already known in the case of amorphous silicon that after bias temperature stress under about 200C, the Vth shift due to the stress is decreased at room temperature as shown in the left figure in Fig.1 because of the charge detrapping from the amorphous silicon and gate insulator. This phenomenon is called "Bias Temperature Stress test." (BTS) It is also already known that after bias temperature stress over about 200C, the Vth shift is frozen at room temperature as shown in the right figure in Fig.1. This phenomenon was discovered by Martin Powell et al. and is called "Thermal Thermal Bias Annealing." It is supposed that the "Thermal Bias Annealing" is due to the charge redistribution in amorphous silicon as a result of charging state change of Si bonds caused by hydrogen redistribution. As hydrogen is mobile over about 200C in amorphous silicon and is immobile under about 200C, the charging state is frozen after cooling down that result in the Vth change. Temperature Time Time

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OLED THRESHOLD VOLTAGE CONTROL

   It is already known in the case of amorphous silicon that after bias temperature stress under about 200C, the Vth shift due to the stress is decreased at room temperature as shown in the left figure in Fig.1 because of the charge detrapping from the amorphous silicon and gate insulator. This phenomenon is called "Bias Temperature Stress test." (BTS) It is also already known that after bias temperature stress over about 200C, the Vth shift is frozen at room temperature as shown in the right figure in Fig.1. This phenomenon was discovered by Martin Powell et al. and is called "Thermal Thermal Bias Annealing." It is supposed that the "Thermal Bias Annealing" is due to the charge redistribution in amorphous silicon as a result of charging state change of Si bonds caused by hydrogen redistribution. As hydrogen is mobile over about 200C in amorphous silicon and is immobile under about 200C, the charging state is frozen after cooling down that result in the Vth change.

Temperature

Time

Time

Amorphous silicon TFT case

Fig.1 Difference between Bias Temperature Stress test and Thermal Bias Annealing

The I-V curve of Organic Light Emitting Diode (OLED) is determined by the difference between metal-organic layer workfunction and between organic layer -organic layer workfunction. For the best light output, and for the charge injection with balanced electron hole recombination, optimum structure, material for each RGB color should be employed. The different structure and material due to the color causes the difference in I-V characteristics (Fig.2). To drive OLED diode with different Vth, it is necessary to have different reference voltage for different color and requires very complicated arrangement of fanout and also requires many driver ICs. Complicated circuit causes low production yield and driver IC for each...