An in‐cell capacitive touch sensor integrated in an LTPS WSVGA TFT‐LCD

In this study, the time response behavior of the amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) to the illumination pulse is analyzed. The mechanism is proposed to correlate the oxygen vacancy reacting with the light-induced electron-hole pairs. The temperature effect on the time response to the illumination pulse is also studied. The higher excitation level, either from light or temperature, results in the similar excited and recovering behaviors. The formulas for the time response are proposed to be possibly used in the simulation for the circuit performance in real situation of illumination, which is important in the development of transparent electronics using a-IGZO TFT. Nowadays, amorphous-silicon (a-Si) thin film transistor (TFTs) have been used widely in flat-panel displays (FPD) in production, with the growing need for large area displays for home entertainment and the full adoption of digital broadcasting. Even with the success, there are still some drawbacks for the TFTs. For example, the low mobility leads to low open area in a pixel because of designing the large size to achieve the high current. For the state-of-art process rule with definite gate length, adopting TFTs with higher mobility is one possible solution to achieve high aperture ratio in a small pixel area without sacrificing the display performance. Therefore, new TFTs with high mobility are needed to replace a-Si TFTs. Among those newly proposed TFTs with high mobility, poly-crystalline silicon (poly-Si) TFTs and amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs attract the most attention.Although poly-Si TFT has μ eff close to 100 cm 2 /V s, it requires additional re-crystallization steps such as excimer-laser annealing, metal seeding or solid phase crystallization. These add more complexity and costs to the process. The substrate size used by poly-Si TFT technology is about 4 generations behind what a-Si TFTs can achieve today, while a-IGZO device encounters no special issue when it comes to the glass size. A-IGZO TFTs have many advantages like low temperature process (below 300• C) and high on/off ratio (∼10 6 ). 1 In addition, it is highly transparent in visible light with transmittance over 90% as illustrated due to wide bandgap (∼3 eV).These properties open up to new applications such as transparent electronics, flexible electronics, and photo sensor.2,3 Even though a-IGZO TFTs exhibit good electrical characteristics and stability in the dark state, the significant electrical instability is observed when they are illuminated. Many article reported threshold voltage (V TH ) shift and mobility change after illumination at different light intensities, and those changes can recover in time. 4,5 In the applications of transparent electronics and photo sensor, the a-IGZO TFTs are expected to operate in the transmission of ambient light with frequently varying intensity. In addition, most of the reports studied the change in the devices under for long-time illumination, 6-8 but the response to the illumination ...

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“…1 In addition, it is highly transparent in visible light with transmittance over 90% as illustrated due to wide bandgap (∼3 eV).…”

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confidence: 99%

The Time Response of the On-Current for the Amorphous In-Ga-Zn-O Thin Film Transistor to the Illumination Pulse

Tai¹,

Chang

Chen

et al. 2014

ECS J. Solid State Sci. Technol.

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“…In-cell touch panels are promising application examples of the capacitance sensors. [57][58][59][60][61] An in-cell touch panel using capacitance sensors is shown in Figure 22. 58 An active-matrix capacitive sensor for use in LCDs as an incell touch panel has been developed.…”

Section: Capacitance Sensormentioning

confidence: 99%

Sensor applications of thin‐film devices originating in display technologies

Kimura

2019

J Soc Info Display

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Thin‐film devices are widely utilized for flat‐panel displays, and the essential advantages of the thin‐film devices are generally large‐area production, various‐material substrate, layered structure, etc. Appropriate applications are flat‐panel displays, and other applications where the abovementioned advantages are available and the disadvantages are acceptable are sensor applications. Moreover, if the sensor devices can be made by thin‐film devices that have been already utilized for flat‐panel displays, they can be made without additional cost. Therefore, thin‐film devices are again promising for sensor applications especially for interactive displays. We are investigating sensor applications of thin‐film devices. Particular in this journal paper, we review sensor applications of thin‐film devices originating in display technologies. The various sensors are visible‐light sensor, infrared‐light sensor, temperature sensor, magnetic‐field sensor, etc. Many research results from many research organizations as well as our research laboratory are introduced.

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“…In particular, an in-cell touch type has drawn lots of attraction by integrating touch sensors into pixel circuits of a display due to the reduction on thickness, weight, and cost. [1][2][3][4][5] However, this integration leads to serious crosstalk between display and touch signals, where the degradation on displayed images and touch performance takes place due to their small gaps. To cope with this crosstalk artifact while increasing the touch reporting rate, an in-cell touch panel conducts touch sensing and displays scanning operations separately based on a time division driving method (TDDM).…”

Section: Introductionmentioning

confidence: 99%

Robust integrated shift register circuit over clock noises for in‐cell touch applications

Seo

Nam

2017

J Soc Info Display

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This paper proposes an integrated shift register circuit for an in‐cell touch panel that is robust over clock noises. It is composed of 10 thin film transistors and 1 capacitor, and the time division driving method is adopted to prevent the negative effect of display signals on the touch sensing. Two pre‐charging nodes are employed for reducing the uniformity degradation of gate pulses over time. In particular, the proposed circuit connects a drain of the first pre‐charging node's pull‐up thin film transistor (TFT) to the positive supply voltage instead of clock signals. This facilitates to lower coupling noises as well as to clock power consumption. The simulation program with an integrated circuit emphasis is conducted for the proposed circuit with low temperature poly‐silicon TFTs. The positive threshold voltage that shifts up to 12 V at the first pre‐charging pull‐up TFT can be compensated for without the uniformity degradation of gate pulses. For a 60‐Hz full‐HD display with a 120‐Hz reporting rate of touches, the clock power consumption of the proposed gate driver circuit is estimated as 7.13 mW with 160 stages of shift registers. In addition, the noise level at the first pre‐charging node is lowered to −28.95 dB compared with 2.37 dB of the previous circuit.

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An in‐cell capacitive touch sensor integrated in an LTPS WSVGA TFT‐LCD

Cited by 25 publications

References 9 publications

The Time Response of the On-Current for the Amorphous In-Ga-Zn-O Thin Film Transistor to the Illumination Pulse

The Time Response of the On-Current for the Amorphous In-Ga-Zn-O Thin Film Transistor to the Illumination Pulse

Sensor applications of thin‐film devices originating in display technologies

Robust integrated shift register circuit over clock noises for in‐cell touch applications

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