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For the first time, we demonstrate an AMOLED pixel circuit on a 13-μm thick plastic film that applies floating-gate organic TFTs FG-OTFTs to compensate for OTFT driving current variations and OLED efficiency degradations. By programming VTH of the FG-OTFTs, we can realize less than 5% spatial non-uniformity and 85%power reduction compared with volt...
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... this paper, for the first time, we demonstrate a FG-OTFT-driven AMOLED pixel circuit for flexible displays as shown in Fig. 1. The pixel circuit enables electrical feedback to tune VTH of the FG-OTFT for compensating OTFT variations and OLED efficiency degradations. Unlike voltage-programming or current-programming [5][6] that require VTH compensation in every frame time, the programmed VTH in our FG-OTFTs can retain for tens of hours and no further VTH ...
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... kept in the Au floating-gate and reduce electrical field from the gate voltage to the organic semiconductor. The effective VTH of the FG-OTFT is therefore increased until the injected electron holes completely escape. More details about our FG-OTFTs can be found elsewhere in [8]. Fig. 4 shows typical voltages of VDATA, VSCAN, VMON, and VSENSE in Fig. 1 for monitoring FG-OTFT non-uniformity and OLED efficiency degradations, as well as programming VTH of the FG-OTFT. In order to monitor the driving current of TD as shown in Fig. 4(a) without being affected by VTH variations of TM, VCAL was set sufficiently close to VTH of TD while VG of TM was set to a higher voltage such as -40V to ...
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... 2 for a given τF and the compensation power PCOMPENSATION (PC) does not directly contribute to driving the OLED, the required PPIXEL for the voltage-programming scheme within the reduced τD in order to achieve the same peak brightness as the proposed VTH programming scheme will therefore increase significantly. Fig. 9 shows the timing diagram and Fig. 10 shows the normalized pixel power consumption PPIXEL for both voltage-programming and VTH programming schemes. Note that PPIXEL in Fig. 10 is calculated by assuming τC equal to 5 μs and the same pixel energy consumption EPIXEL under the same τF for both cases. While the proposed VTH programming scheme using FG-OTFTs does not require the ...
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... voltage-programming scheme within the reduced τD in order to achieve the same peak brightness as the proposed VTH programming scheme will therefore increase significantly. Fig. 9 shows the timing diagram and Fig. 10 shows the normalized pixel power consumption PPIXEL for both voltage-programming and VTH programming schemes. Note that PPIXEL in Fig. 10 is calculated by assuming τC equal to 5 μs and the same pixel energy consumption EPIXEL under the same τF for both cases. While the proposed VTH programming scheme using FG-OTFTs does not require the VTH compensation cycle and consumes negligible compensation power during the VTH programming process, the voltage-programming scheme ...
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... this paper, for the first time, we demonstate a FG-OTFT driven AMOLED pixel circuit on a 80-μm thick polyimide plastic film for compensating OTFT process variations and OLED efficiency degradations. The die photo of the proposed FG-OTFT pixel-circuit is shown in Fig. 11. In our test sample, we prepared six identical pixels allocated as a 2x3 array. After applying the electrical stress to the driving FG-OTFTs, the overall spacial non-uniformity of the driving FG-OTFTs was minimized from 14% to be less than 5%. Compared with the conventional voltage-programming compensation scheme, the pixel power ...
Citations
... One such example is an image classifier application where the floating-gate memories are used for storing weight values [13]. Floating-gate can also be used for post-fabrication tuning to encounter device variation [14]. One challenge for floating-gate memory based sensor array with local functional units is to find a way to program the floating-gate devices individually, Our proposed CMOS based multiplier scheme allows us to access the three terminal of a floating-gate device, hence implementation of a virtual memory array becomes possible. ...
... X-axis shows the change of applied gate voltage to the nFET. pFET gate voltage is applied according to (14). In the first scenario, all the sensors are assumed to have same values meaning there is no unevenness in the surface. ...
Artificial neurons are introduced for local data processing in a large area sensor device, thereby reducing multiple sensor outputs to 1-bit digital output. To reduce the area overhead and layout complexity due to the artificial neuron array, a 2-transistor multiplier using organic floating-gate pFET is proposed. Each artificial neuron has multiple organic floating-gate pFETs embedded in it. A virtual scalable floating-gate based memory architecture is realized for selective programming of each floating-gate pFET. Threshold voltage tuning is utilized to realize both of the positive and the negative weight values for a neuron. A flexible interface pressure monitoring device with pressure-sensitive rubber sheet is developed for pressure ulcer prevention to show the feasibility of our concept. A 50 mm² organic sheet integrating $2x 2$ neuron array is fabricated with 2-V organic CMOS transistors. Selective floating-gate programming and neuron operation are successfully demonstrated.
We have demonstrated an ultraflexible active matrix organic LED pixel circuit on 13-μm thin-film plastics for applications to medical sensors and treatments. The circuit that applies printed floating-gate organic transistors can compensate LED brightness variations and degradation for more than 6 months. The 230times230 mm2 printed active matrix circuit comprises 64times64 screen-printed organic 2-transistor-1-capacitor cells.
An AMOLED panel driven by an OTFT-backplane is an attractive display because OTFTs and OLEDs use organic materials with unique characteristics such as low temperature and solution processing ability, and thus are able to implement the key features of future displays. In this study we applied some printing technologies to fabricate an OTFT-backplane for AMOLEDs. Screen printing combined with photolithography with Ag ink was used for the gate electrodes and scan bus lines and contact pads. Ag metal lines with a width of 20 μm and thickness of 60 nm and resistivity of 3.0 × 10−5 Ω cm were achieved. Inkjet printing was applied to deposit TIPS-pentacene as an organic semiconductor. The OTFT-backplane using the Ag gate electrodes and TIPS-pentacene exhibited uniform performance over 17,500 pixels on a 7 in. panel. The mobility was 0.31 ± 0.05 cm2/V s with a deviation of 17%. The AMOLED panel successfully demonstrated its ability to display patterns.
Editor's note:In this review article, the authors survey several thin-film transistor (TFT) technologies for flexible electronics of the future. The review's focus centers on the reliability issues of these new devices compared to those of classic silicon CMOS. In addition, the article examines different digital and analog design techniques, which are discussed within the context of robust circuit design.—Dimitris Gizopoulos, IEEE Design & Test Tutorial Articles Department Editor; University of Athens
