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Micro-LED has been considered the ultimate of what emissive displays can offer. In theory, these displays should not have any of their predecessor challenges. However, the reality is different and several major challenges should be addressed priorr to micro-LED makes a huge entry.

Amorphous oxide semiconductor thin film transistors and sensors constitute fundamental building blocks for a new generation of applications ranging from interactive displays and imaging to future electronic systems that are unconstrained by form factor. This makes the quest for high mobility materials processed at low temperatures even more compelling, to enable the layering of circuits and systems on plastic and possibly even paper substrates. Transparency is also an attractive feature that enables seamless embedding of electronics for the immersive ambient. This paper reviews the current status of the ubiquitous oxide semiconductor technology for flexible and transparent interactive displays, along with demonstrated examples of continuous thin film and nanowire systems for the transistor and sensor. Issues related to photo-sensing and active matrix operation are discussed along with solutions addressing the problem of threshold voltage instability and its compensation for fast recovery, particularly after light stress. Physics-based compact models for expedient design and simulation of analog and digital circuits are reviewed along with examples of key system building blocks. Finally we attempt to conceptualize a thin film transistor (TFT)-based fully heterogeneously integrated and autonomous system that can be realized using a combination of oxide and other technological routes.

The two major backplane technologies for AMOLED displays are LTPS and oxides. Despite their similarities, the differences are significant requiring intricate design considerations and compensation techniques to achieve good display uniformity and lifetime while eliminating second order effects associated with IR drop, ground bouncing, and parasitic capacitance. This paper presents a study in contrasts between LTPS and oxide backplane technologies from the standpoint of system design and compensation techniques.

Although IGNIS technology support any type of backplane, we believe a-Si:H backplanes have significant advantages for a wide range of applications. This paper studies how the first product-ready a-Si:H AMOLED works for applications ranging from mobile displays to large high-frame rate displays intended for TV.

A polarizer-less OLED is introduced with 30% improvement in efficiency. Also, the new OLED structure provides integrated multi-touch, power recycling/generating, and non-uniformity /aging self-calibration capabilities.

This work reports an integration process for hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) backplanes on flexible plastic substrates that attempts to reduce the large misalignment between the successive patterned layers in fabrication. Here, a double-sided adhesive tape is used to attach the plastic substrate to a rigid carrier. The results indicate a reduction of overlay misalignment from 22 μm on free-standing foil to 2 μm when laminated to a rigid carrier for five consecutive mask layers. Electrical characteristics of the fabricated a-Si:H TFTs on 3" round plastic substrates show an ON/OFF current ratio of over 108, field-effect mobility of 0.8 cm2/V · s, and gate leakage current of 10-13 A.

This work reports on the performance and stability of bottom-gate In2O3-TFTs with PECVD silicon dioxide gate dielectric. A highly-resistive amorphous In2O3 channel layer was deposited at room temperature by reactive ion beam assisted evaporation (IBAE). The field-effect mobility of the n-channel TFT is 33 cm2/V-s, along with an ON/OFF current ratio of 109, and threshold voltage of 2 V. Device stability was demonstrated through measurement of the threshold voltage shift during long-term gate bias-stress and current stress experiments. Device performance, including stability, together with low-temperature processing, makes the indium-oxide TFT an attractive candidate for flexible transparent electronics, and display applications.

A reliable driving scheme that can compensate for the inherent instability of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) is essential for implementation of large-area devices including displays and sensor arrays for bio-imaging applications. In particular, for high precision and high-resolution devices, the technique should be accurate and fast. A new driving scheme is presented that enables control of the DC and transient shift in the threshold voltage (V T ) and gate voltage of drive/amplifier TFT, while fulfilling the timing requirements for the different applications. The transient shift in the gate voltage has been known to contribute as much as 10% error in controlling the DC shift in the V T whereas it is less than 0.5% for the driving scheme presented here.

We present a new simple and low cost pixel circuit and driving scheme for the a-Si AMOLED displays using conventional AMLCD drivers. Measurement results show significant stability and high immunity to temperature and mobility variations which makes the pixel circuit and driving scheme attractive for implementation in different technologies. A 9-inch a-Si AMOLED display fabricated based on this driving scheme shows high uniformity and long lifetime.

This paper presents the current status of oxide semiconductor technology for applications ranging from interactive displays to imaging systems with a strong focus on device-circuit interaction to compensate for material weaknesses and issues related to non-uniformity, instability, and persistent photoconductivity.

Hydrogenated amorphous silicon (a-Si:H) technology is interesting for large-area active matrix structure due to its good uniformity over large-area, low-temperature, and low-cost fabrication, and its industrial accessibility. However, the circuits implemented in this technology suffer from the instability of the material under prolonged bias stress. To improve the circuit stability, we present a circuit design technique based on the stability of a-Si:H thin film transistors (TFTs) under short-term bias stress. Here, an a-Si:H local current source (LCS) is used to adjust the circuit current bias. Since the LCS circuit is under stress for a small fraction of operation time, its current remains stable. The measurement and analysis of the LCS circuit indicate that the a-Si:H TFT is stable under short-term bias stress for over 50000h. Also, we present a pixel circuit based on this technique for active matrix organic light emitting diode displays.

Herein, we describe a novel integrated biosensor for performing dielectric spectroscopy to analyze biological samples. We analyzed biomolecule samples with different concentrations and demonstrated that the solution's impedance is highly correlated with the concentration, indicating that it may be possible to use this sensor as a concentration sensor. In contrast with standard spectrophotometers, this sensor offers a low-cost and purely electrical solution for the quantitative analysis of biomolecule solutions. In addition to determining concentrations, we found that the sample solution impedance is highly correlated with the length of the DNA fragments, indicating that the sizes of PCR products could be validated with an integrated chip-based, sample-friendly system within a few minutes. The system could be the basis of a rapid, low-cost platform for DNA characterization with broad applications in cancer and genetic disease research.

For some applications such as high-resolution AMOLED displays for TVs and monitors, as well as for highly sensitive imaging modalities such as radiography and radiotherapy, the backplane should compensate for all the effects caused by the aging or mismatches to achieve the intended accuracy (e.g. less than 0.5% differential aging for a TV screen). While the entire proposed driving scheme compensates only for the static effect of V T -shift (i.e. drop in the pixel current/gain), the transient effects such as charge injection and clock feed-through can cause up to 10% error in the pixel characteristics. To solve this issue, we introduce a calibration technique capable of controlling the transient effects as well as the static effect of the V T -shift (mismatches) [108, 112, 113]. Moreover, a hybrid approach is introduced that takes advantage of both calibration technique and in-pixel compensation. Time-dependent charge injection and clock feed-through To compensate for the V T -shift/mismatch, the compensation techniques [64, 67] lead to a modification in the gate voltage of the drive TFT to provide a constant overdrive voltage. However, as a consequence of this change in the gate voltage, clock feed-through and charge injection associated with the parasitic capacitances change over time. Since the storage capacitor cannot be large due to the mandated frame time and aperture ratio, the parasitic capacitances stemming from the overlap of the gate over the drain and source become comparable. Moreover, the threshold voltage of the switch TFTs decreases since they are under negative bias stress during most of the frame time [58]. Consequently, the charge profile of their channels changes for a given programming voltage inducing a time-dependent error.

This chapter presents accelerated programming/resetting of active pixel circuits based on bias currents presented in [87]. The settling time in current programming depends strongly on the V T of the drive transistor and initial line voltage ( V 0 ). Figure 3.1 shows the settling time of the pixel circuit depicted in Figure 2.5(a) as a function of the initial voltage. It is evident that the settling time changes as the initial voltage changes. As a result, since the voltage of the previous pixel remains on the data line, the programming of the new pixel is affected. Pre-charging the data lines to a specific voltage can control the effect of the initial voltage, but this can increase the power consumption considerably. Moreover, initial voltage is a function of the V T . Thus, the settling time cannot be managed by a fixed pre-charging voltage, because the value of V T is varying. Thus, a dynamic line pre-charging scheme, coupled with a large current, is required to improve the settling time. To develop this driving scheme, a fix current is required to program the pixels so that the initial voltage becomes independent of the pixel content. Also, in-pixel current reduction/division is used to adjust the pixel current accordingly. This driving scheme is called the current-biased voltage-programmed (CBVP) scheme [86, 87].

Providing a reliable and consolidated treatment of the principles behind large-area electronics, this book provides a comprehensive review of the design challenges associated with building circuits and systems from thin-film transistors. The authors describe the architecture, fabrication and design considerations for the principal types of TFT and their numerous applications. The practicalities of device non-ideality are also addressed and the specific design considerations necessitated by instabilities and non-uniformities in existing fabrication technologies. Containing device-circuit information, discussion of electronic solutions that compensate for material deficiencies, and design methodologies applicable to a wide variety of organic and inorganic disordered materials, this is an essential reference for all researchers, circuit and device engineers working on large-area electronics.

Active-matrix organic light emitting diode displays are prone to significant V TH and mobility variations in low-temperature polycrystalline-silicon thin-film transistors. A low-cost characterization of these variations can lead to a practical external calibration and simulation of the display non-uniformity. This paper proposes a generic methodology based on principal component analysis, relying on the display current levels corresponding to applied characterization images. This technique results in simultaneous characterization of the V TH and mobility for the entire active matrix. Measurement results show that taking advantage of spatial correlation leads to 100 times reduction in characterization time with less than 30% relative error.

An amorphous silicon (a-Si:H) thin film transistor (TFT) circuit designed for charging of an energy storage device using a photovoltaic (PV) array is presented. The TFT circuit is fabricated at plastic compatible temperatures (∼150°C) and as such can easily be integrated within a range of platforms including flexible displays. The circuit provides a high degree of output voltage stability over a range of light intensities and device stress.

The active matrix organic light emitting diode (AMOLED) display is a strong candidate for the next generation display because of attributes such as low power consumption, wide viewing angle, highly saturated colors, fast response, and high contrast ratio. More importantly, its structural simplicity (compared to the active matrix liquid crystal display) gives it the potential for low fabrication costs. Since the OLED is a current driven device, an active matrix of thin film transistors (TFTs) is needed to provide a programmable current source at each pixel [1]. Thus, OLED luminance becomes extremely sensitive to the temporal instability and spatial non-uniformity of the TFTs which can result in Mura, image sticking, and reduced lifetime [1–4].

In recent years, the increasing use of active matrix flat-panel displays and bio-medical imagers in commercial electronic products has drawn a significant attention to thin-film transistors (TFT) and technologies. TFTs on amorphous- and poly-silicon as well as newly emerging organic, transparent metal oxide and nano-composite semiconductor technologies are becoming increasingly common. For example, flat panel displays are finding widespread use in many products such as cellular phones, personal digital assistants (PDAs), camcorders, laptop personal computers (PCs), to name a few. The active matrix display is composed of a grid or matrix of picture elements called as “pixels”. Thousands or millions of these pixels together create an image on the display, in which the TFTs act as switches to individually turn each pixel. More increasingly TFTs are starting to be used as analog circuit elements for rudimentary signal conditioning. Therefore, physically-based compact modeling of TFTs for circuit simulation is crucial to accurately and reliably predict TFT behavior in the active matrix. A concentrated R&D effort is critical for developing physically-based compact TFT models for emerging thin-film technologies, and significant R&D efforts along these lines are underway world-wide.

We report on directly deposited plasma-enhanced chemical vapor deposition (PECVD) nanocrystalline silicon (nc-Si:H) ambipolar thin-film transistors (TFTs) fabricated at 260 °C. The ambipolar operation is achieved adopting Cr metal contacts with high-quality nc-Si:H channel layer, which creates highly conductive Cr silicided drain/source contacts, reducing both electron and hole injection barriers. The n-channel nc-Si:H TFTs show a field-effect electron mobility (meFE) of 150 cm2/Vs, threshold voltage (VT) ~ 2 V, subthreshold slope (S) ~0.3 V/dec, and ON/OFF current ratio of more than 107, while the p-channel nc-Si:H TFTs show a field-effect hole mobility (mhFE) of 26 cm2/Vs, VT ~ -3.8 V, S ~0.25 V/dec, and ON/OFF current ratio of more than 106. Complementary metal-oxide-semiconductor (CMOS) logic integrated with two ambipolar nc-Si:H TFTs shows reasonable transfer characteristics. The results presented here demonstrate that low-temperature nc-Si:H TFT technology is feasible for total integration of active-matrix TFT backplanes.

This paper describes a low-power driving scheme along with a pixel circuit based on hydrogenated amorphous silicon (a-Si:H) technology for active matrix organic light emitting diode (AMOLED) displays. The driving scheme can provide different current levels for the OLED while compensating for long-term (and gradual) instabilities caused by material defect metastability which will make it amenable for use in AMOLED displays. Moreover, since the threshold voltage is known in this method, it can be used to compensate for the time-dependent errors of the charge injection and clock feed-through effects. Therefore, the error for a 3V shift in the VT of T1 is almost zero. More importantly, it has low power consumption because the line capacitance is charged just one time during the programming cycle. For example, the total power consumption of a QVGA array (240*320) is expected to be less than 1.5W.

This paper presents a novel digital circuit design methodology that can support high-performance and low-power applications. In this method, reusing past internal voltages, signals are charged to Vdd/2 during the pre-charge cycle, so that the voltage of a signal is changed by just Vdd/2 during the evaluation cycle, resulting in a significant reduction in power consumption and propagation delay. The simulation results performed in 0.18/spl mu/m CMOS technology, demonstrate that the new circuit has three times improvement in terms of propagation delay in comparison to the equivalent domino dynamic logics. More importantly, its power consumption is 2.4 times less than that of the domino logics counterpart.

A unique measurement and compensation technology for AMOLED high definition television is presented. The technique electrically measures every TFT and OLED in the backplane, useful for inspection and diagnostics in the factory, and subsequent compensation of mura, TFT- and OLED-degradation.

The field effect (FE) mobility of thin film transistors is normally extracted using static measurement methods, which inherently rely on the assumption that the device remains stable during the measurement duration. However, these devices, particularly those based on emerging materials, can show large instability during the measurement, typically exhibiting hysteresis in the static characteristics. This letter looks at the effect of threshold voltage shift in FE mobility extracted using the conventional method, and introduces an alternative and more accurate technique of measuring device characteristics. The technique decouples the effect of transient phenomena, thus permitting extraction of the true device FE mobility, which turns out to be either over or underestimated depending on the magnitude and direction of threshold voltage shift.

Indium oxides were deposited by reactive ion beam assisted e-beam evaporation at room temperature. A material study was conducted through a variety of material characterization including crystal structure, electrical properties, optical properties, and chemical composition, along with an investigation of material properties as a function of primary deposition parameters such as ion flux and deposition rate. Implementing the developed semiconducting indium oxide as a channel material, the authors further demonstrated high-performance indium oxide thin-film transistors (TFTs) with conventional silicon dioxide gate dielectric derived by plasma-enhanced chemical vapor deposition (PECVD). The n-channel TFT has a threshold voltage of ∼2.0 V, a field-effect mobility of 33 cm2/V s at a gate bias of 20 V, an ON/OFF current ratio of 108, and a subthreshold slope of 2.0 V/decade. The stability study displays a small threshold voltage shift of ∼0.6 V under a 60 h constant current stress condition. The TFT reported he...

MaxLife™ is a breakthrough backplane solution for AMOLED television. We demonstrate a compensating technology with a prototype that monitors and corrects for the OLED and TFT aging at each pixel for expected lifetimes of 50,000h+. This provides a tremendous boost in realizing low-cost AMOLED TVs using amorphous or poly-Silicon backplanes.

The instability and low mobility of amorphous silicon (a-Si) TFTs demand new driving schemes for large and medium size AMOLED displays. This paper presents a new driving scheme with fast-settling that also compensates for the instability of a-Si TFTs.

Amorphous silicon AMOLED displays are almost ready for mass production and will be found in all display applications from high resolution cell phone to HDTV. But before commercialization can occur, the problems of lifetime and image sticking need to be overcome. When it comes to pixel circuit design, there is no one-size-fits-all solution. Several drive schemes and pixel circuits are presented, each with unique advantages, and each suited for a particular application. All leverage amorphous silicon manufacturing infrastructure which leads to the lowest cost position for AMOLEDs on glass.

This paper reviews the importance of device-circuit interactions (DCI) and its consideration when designing thin film transistor circuits and systems. We examine temperature- and process-induced variations and propose a way to evaluate the maximum achievable intrinsic performance of the TFT. This is aimed at determining when DCI becomes crucial for a specific application. Compensation methods are then reviewed to show examples of how DCI is considered in the design of AMOLED displays. Other designs such as analog front-end and image sensors are also discussed, where alternate circuits should be designed to overcome the limitations of the intrinsic device properties.

Organic light emitting diode (OLED) displays are a serious competitor to liquid crystal displays in view of their superior picture quality, higher contrast, faster on/off response, thinner profile, and high power efficiency. For large area and/or high-resolution applications, an active matrix OLED (AMOLED) addressing scheme is vital. The active matrix backplane can be made with amorphous silicon (a-Si), polysilicon, or organic technology, all of which suffer from threshold voltage shift and/or mismatch problems, causing temporal or spatial variations in the OLED brightness. In addition, the efficiency of the OLED itself degrades over time. Despite these shortcomings, there has been considerable progress in development of AMOLED displays using circuit solutions engineered to provide stable and uniform brightness. Indeed the design of AMOLED pixel circuits, particularly in low-mobility TFT technologies such as a-Si, is challenging due to the stringent requirements of timing, current matching, and low voltage operation. While circuit solutions are necessary, they are not sufficient. Process improvements to enhance TFT performance are becoming inevitable. This paper will review pertinent material requirements of AMOLED backplanes along with design considerations that address pixel architecture, contact resistance, and more importantly, the threshold voltage stability and associated gate overdrive voltage. In particular, we address the question of whether conventional PECVD can be deployed for high mobility and high stability TFTs, and if micro-/nano-crystalline silicon could provide the solution.