Introduction to quality engineering : designing quality into products and processes

The field of flexible electronics has rapidly expanded over the last decades, pioneering novel applications, such as wearable and textile integrated devices, seamless and embedded patch-like systems, soft electronic skins, as well as imperceptible and transient implants. The possibility to revolutionize our daily life with such disruptive appliances has fueled the quest for electronic devices which yield good electrical and mechanical performance and are at the same time light-weight, transparent, conformable, stretchable, and even biodegradable. Flexible metal oxide semiconductor thin-film transistors (TFTs) can fulfill all these requirements and are therefore considered the most promising technology for tomorrow's electronics. This review reflects the establishment of flexible metal oxide semiconductor TFTs, from the development of single devices, large-area circuits, up to entirely integrated systems. First, an introduction on metal oxide semiconductor TFTs is given, where the history of the field is revisited, the TFT configurations and operating principles are presented, and the main issues and technological challenges faced in the area are analyzed. Then, the recent advances achieved for flexible n-type metal oxide semiconductor TFTs manufactured by physical vapor deposition methods and solution-processing techniques are summarized. In particular, the ability of flexible metal oxide semiconductor TFTs to combine low temperature fabrication, high carrier mobility, large frequency operation, extreme mechanical bendability, together with transparency, conformability, stretchability, and water dissolubility is shown. Afterward, a detailed analysis of the most promising metal oxide semiconducting materials developed to realize the state-of-the-art flexible p-type TFTs is given. Next, the recent progresses obtained for flexible metal oxide semiconductor-based electronic circuits, realized with both unipolar and complementary technology, are reported. In particular, the realization of large-area digital circuitry like flexible near field communication tags and analog integrated circuits such as bendable operational amplifiers is presented. The last topic of this review is devoted for emerging flexible electronic systems, from foldable displays, power transmission elements to integrated systems for large-area sensing and data storage and transmission. Finally, the conclusions are drawn and an outlook over the field with a prediction for the future is provided.

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Metal oxide semiconductor thin-film transistors for flexible electronics

In advanced technology node, not only process variations but also aging effects have critical impacts on circuit performance. Most of existing works consider process variations and aging effects separately while building the corresponding behavior models. Because of the time-varied circuit property, parametric yield need to be reanalyzed in each aging time step. This results in expensive simulation cost for reliability analysis due to the huge number of circuit simulation runs. In this paper, an incremental Latin hypercube sampling (LHS) approach is proposed to build the stochastic behavior models for analog/mixed-signal (AMS) circuits while simultaneously considering process variations and aging effects. By reusing previous sampling information, only a few new samples are incrementally updated to build an accurate stochastic model in different time steps, which significantly reduces the number of simulations for aging analysis. Experiments on an operational amplifier and a DAC circuit achieve 242x speedup over traditional reliability analysis method with similar accuracies.

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Incremental Latin hypercube sampling for lifetime stochastic behavioral modeling of analog circuits

The flexible electronics is promising in the area of the Internet of Things and wearable devices and the thin-film transistor (TFT) technologies are crucial for flexible electronics. Among them, the zero- $V_{\text {GS}}$ load TFT circuits are widely used for its simple structure and high gain merits. However, the yield model is lacking for zero- $V_{\text {GS}}$ load TFT circuits. In this paper, the analytical noise margin model for the zero- $V_{\text {GS}}$ load TFT NAND gate and NOR gate is derived. Based on that, a simple, accurate, and highly scalable yield model for the combinational TFT logic circuits based on standard cell library is further proposed. ISCAS’85 benchmark circuits are used to validate the yield model. Compared with Monte Carlo simulation, the model achieves 3–4 orders of magnitude speedup with comparative results.

Noise Margin Modeling for Zero- $V_{\text {GS}}$ Load TFT Circuits and Yield Estimation

Discussed is a flexible organic light emitting display device. The flexible organic light emitting display device according to an embodiment includes a panel, a data driver configured to drive data lines included in the panel, a gate driver configured to drive gate lines included in the panel, a sensing unit, and a controller. The sensing unit may sense bending of the panel in a blank period of one frame period by using a pixel driving circuit included in each of a plurality of pixels included in the panel, for sensing a characteristic change of a driving transistor driving an organic light emitting diode included in each of the plurality of pixels, the one frame period including the blank period and a display period. The controller may sense the characteristic change of the driving transistor or analyze whether the panel is bent, based on pieces of sensing data transferred from the sensing unit.

Flexible organic light emitting display device

This paper presents a SPICE-based simulator, FlexiAnalyzer, for flexible thin-film transistor (TFT) circuits. This simulator performs four types of analysis: yield analysis, aging analysis, performance analysis, and weak spot analysis. This simulator considers three important effects: 1) threshold voltage variation of manufacturing process; 2) threshold voltage shift due to aging effect; and 3) mobility change due to bending effect. Six different OLED pixel drivers designed in 8- μm amorphous silicon TFT technology were used in simulation results. The proposed tool provides a good solution for designers to evaluate the performance and yield of flexible TFT circuits.

Flexible TFT Circuit Analyzer Considering Process Variation, Aging, and Bending Effects

This paper presents a yield optimization tool, FlexiOptimizer ,
for flexible thin-film transistor (TFT) circuits. FlexiOptimizer considers
three important effects: (1) process variation; (2) aging effect; and (3)
bending effect. This SPICE-based optimizer applies response surface methodology
(RSM) and orthogonal array (OA) techniques to size transistors so the yield
is improved in aged and bent condition. This tool is demonstrated on two different
designs: organic light emitting diode (OLED) pixel drivers and differential
operational amplifiers (OPAMPs), in both amorphous silicon (a-Si) and Indium-Gallium-Zinc-Oxide
(IGZO) TFT technologies.

Hung-Yi Li

Papers

Flexible TFT Circuit Analyzer Considering Process Variation, Aging, and Bending Effects

A Flexible TFT Circuit Yield Optimizer Considering Process Variation, Aging, and Bending Effects