"18th International Display Workshops (IDW '11)" (December 7-9, 2011, Nagoya International Conference Hall) staggered the meeting time of the active matrix (AMD) and the organic EL (OLED) during the meeting, so the author listened It's very enjoyable to have all the publications I want to hear. If the meeting party can stagger the time of the related meeting like this time, it would be too grateful.
But this IDW also has some incomprehensible points, that is, "OLED2" has Organic TFT meeting (organic TFT meeting), and "AMD5" has also become Organic TFT meeting, what standard does Organic TFT define in the end, it belongs to OLED The class is still AMD, which is a bit confusing. The author hopes that, including content related to flexible displays, it is best to be able to clarify the criteria for classifying publications in the future. Personally, it is also a good choice to increase joint meetings.
Organic TFTs, oxide TFTs, and transparent displays were published one after another-the last day of the AMD meeting
At the organic TFT conference, Japan Toppan Printing was first published, introducing the printing technology used to form the organic TFT (paper number: AMD5-1). The company stated that it is suitable to use offset printing when forming the gate electrode and the source-drain electrode, flexographic printing when forming the organic channel layer, and screen printing when forming the interlayer insulating film and the pixel electrode. Offset printing has the characteristics of high resolution (supporting 5μm line spacing), high throughput and large area operation. Flexographic printing has the characteristics of good uniformity, high ink utilization efficiency, excellent pattern reproduction accuracy, and can avoid impurity pollution. Using these printing technologies, the company has trial-produced 5.35-inch 150ppi, 2-inch 50ppi, and 11-inch 73ppi organic TFT arrays on PEN substrates without using any photolithography process, and made it from Taiwan ’s E Ink film The flexible electronic paper confirmed the working condition.
The University of Tokyo and others have published organic TFT arrays for organic EL driving that can use floating gates to control Vth characteristics (Paper No. AMD5-3). The characteristics are controlled by applying a pulse waveform with a width of 50 ms to the floating gate at a voltage of 60 V which is three times the normal gate voltage. The pixel circuit is of the 3T1C (3 transistors, 1 capacitor) type, and is driven while monitoring the deviation of the characteristics of the driving TFT and the deterioration of the organic EL. The University of Tokyo said that compared with the conventional external compensation circuit, the circuit scale can be further reduced.
The Asahi Glass subsidiary of Japan and the Tokyo Institute of Technology have published a method to improve the reliability of oxide TFTs-glass powder sealing technology that seals the entire device (Paper No. AMD6-5L). The value of the water vapor transmission rate WVTR fell below 10-6g / m2 / day. It is said that the reliability of amorphous IGZO (a-IGZO) TFTs has been greatly improved after this glass sealing. The amorphous IGZO (a-IGZO) TFT was subjected to a 5μA room temperature rated current impact test for 20 hours and the Vth drift was detected. The results showed that it was 0.3V when glass sealing was implemented, and 1.5V when glass sealing was not implemented. Even under the conditions of 60 ° C and 90% humidity, the Vth drift amount dropped to 0.5V after 20 hours. The TFT is a back-channel etching type with a bottom gate structure. It has been confirmed that even without a passivation film, such a large reliability improvement effect can be obtained only by the glass sealing film.
South Korea ’s Samsung Electronics announced the significance of developing a transparent liquid crystal display (paper number: AMD7-2). Although this is a presentation at the application conference, it basically does not involve technical content, but it can be deeply understood from the severe situation of the liquid crystal industry and the great expectations for the new application of transparent liquid crystal displays, which is very interesting. The LCD industry is looking forward to the emergence of new huge shockwaves due to the lack of growth in the highly anticipated three-dimensional (3D) TVs and smart TVs as the next round of shockwaves for LED backlight LCD TVs. Samsung is optimistic about transparent LCD monitor. The company used a large number of schematic diagrams of specific application examples to demonstrate, the content is very exciting. As a device that can realize a new type of digital signage and a new type of human-machine interface, the transparent liquid crystal display is expected to be well received in the market. However, calmly think about the various performance indicators required by this display and the cost of achieving these indicators. It may be very difficult to say that this display can set off a huge shock wave.
Fujifilm has released a high-performance IGZO TFT with a mobility of more than 40cm2 / Vs (Paper No. AMD8-4L). According to the company, through the dry annealing treatment with oxygen stable isotope 18O, the diffusion state of oxygen into the IGZO film was evaluated, and it was obtained that the oxygen began to diffuse into the film at a temperature above 350 ℃ and reached at 450 ℃ 15nm deep results. Based on this result, the company trial-produced TFTs in the following two configurations. First, a 100-nm-thick oxidized SiO2 film is formed on a p-type silicon wafer, which is used as a gate electrode and a gate insulating film. Then the first layer, the In1.85Ga0.15ZnO4 film with a thickness of 5 nm, is formed as the main carrier layer with high carrier density, and then the second layer, the In0.5Ga1.5ZnO4 film, is formed as the A resistive film. The company conducted experiments using two types of TFTs with 8nm (Type A) and 50nm (Type B) thickness of the first resistive film. Annealing was performed in the above-mentioned state under a dry oxygen mist environment at 450 ° C. The Type A TFT was laminated with an In0.5Ga1.5ZnO4 film after annealing to achieve a total film thickness of 50 nm. Finally, a mask is used to form Ti / Au source-drain electrodes.
With this structure, the mobility of Type A reaches 41.8cm2 / Vs, and the mobility of Type B reaches 38.4cm2 / Vs. Although the difference in mobility between the TFTs of the two structures is small, there is a big difference in the change in light impact. Especially in the range of λ <400nm, the Vth drift of Type A is -0.05V, while the Vth drift of Type B reaches -0.38V. Based on the results of these experiments, Fujifilm concluded that controlling the amount of oxygen diffusing into the IGZO film can contribute to improving the mobility and light impact resistance of the TFT.
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