The Flexible TFT circuit covers a wide spectrum of applications including flexible display, e-paper, printed RFID and others. In ADRC, the integration of system especially driver in flexible display with a-IGZO TFT are studied.

1) Flexible substrates
Polyimide (PI) can stand high processing temperatures is one preferable candidate plastic substrate for fabricating flexible electronics. During the devices fabrication, glass substrates are used as the cattier substrate, on which the PI imbedded with grapheme oxide (GO) and carbon nanotube (CNT) are coated. The flexible substrates are then realized after the detachment as shown in Figure 1.

Figure 1. a-IGZO TFT based circuits on PI substrate

2) Ring Oscillator

Figure 2. shows the schematic (a), the optical image (b), and the output waveform (c) of the fabricated ring oscillator. For a VDD of 20 V, the high voltage (Vhigh) and the low voltage (Vlow) of the waveform are 12.84 and 2.53 V, respectively, and the circuit operates at a frequency of 94.8 kHz, which corresponds to a propagation delay time of 0.48 μs/stage. This is only two times slower than the fastest AOS TFT-based ring oscillators on glass substrates.

 

Figure 2. (a) Schematic of an 11-stage ring oscillator
(b) the optical image
(c) output characteristics of the fabricated ring oscillator.

3) Shift Register
A high speed and ultra-narrow 40 um-pitch shift register was designed and fabricated with a-IGZO TFT on PI substrate. Figure 3 shows the (a) schematic design, (b) timing diagrams and (c) optical image of the shift register. The shift register could be operated under mechanical bending radius of 2mm, with the output voltage, rise time and fall time of 14.7 V, 0.95 us and 0.75 us at the supply voltage (VDD) of 15 V, the clock frequency of the shift register approached 166.7 kHz as shown in figure 3 (d).

 

Figure 3. The layout of array and unit pixel

Related invited/plenary talks by Prof Jin Jang

1) “Printed TFT curcuits on plastic with solution process”, 2012 MRS Spring Meeting, (2012.04.09~13, Moscone West Convention Center, San Francisco, USA)
2) “Robust TFT backplane for flexible AMOLED”, SID Display Week (2012.06.03-08, Boston Convention and Exhibition Center, USA)
3) Printed TFT and circuits based on organic semiconductor on flexible substrate”, SPIE 2012, (2012.08.12-16, San Diego Convention Center, San Diego, USA)
4) "Stability & Flexibiity of a-IGZO TFT on Plastic & It's Application to TFT Circuits", 7th International Thin-Film Transistor Conference (2011.03.03-04, Cambridge, UK)