User-interactive electronic skin for instantaneous pressure visualization

Efficient micro-pixel array of small molecule organic light-emitting diodes (OLEDs) has been fabricated by an imprinting technique which uses a polymer replica. To confirm the effect of the oxygen plasma for removing the residual layer, the performance of two kinds of OLEDs with varying thicknesses of resin as the micro-pixel array, have been compared. The measured results of the OLEDs have shown comparable device performances that are significantly characterized depending on the residues on the substrate. The performance of enhanced device has achieved efficiencies of 3.6 cd/A and 1.9 lm/W at 20 mA/cm2.

The luminance stability and lateral leakage play an important role in the organic light-emitting diodes (OLEDs) array for high-resolution displays application, but less research was presented to optimize the problems effectively. Herein, we reported hybridized plasma treatments with hydrogen passivation to oxygen treated indium tin oxide (ITO) surfaces of OLEDs array, revealing an outstanding performance in this study. According to the added hydrogen as a deactivated function to further modify the surfaces of ITO, we finally obtained a high and stable work function simultaneously leading to better luminance stability. It was proven to change the waste into a treasure that the hydrogen passivation had arrested the activating reactions at the interfaces which were always ignored in the traditional methods. And we also acquired a disappearance of the optoelectronic crosstalk by the next-door devices via the suppressed interface charge migration to keep low lateral leakage. It was presented that eliminating the contaminants and mobile ions was induced by the hybridized plasma treatments. The research opens the possibility of considering the interface influences of self-luminous devices array for the actual application.

In this paper, we report a 3.4-in. flexible active matrix organic light emitting display (AMOLED) display with remarkably high definition (quarter high definition: QHD) in which oxide thin film transistors (TFTs) are used. We have developed a transfer technology in which a TFT array formed on a glass substrate is separated from the substrate by physical force and then attached to a flexible plastic substrate. Unlike a normal process in which a TFT array is directly fabricated on a thin plastic substrate, our transfer technology permits a high integration of high performance TFTs, such as low-temperature polycrystalline silicon TFTs (LTPS TFTs) and oxide TFTs, on a plastic substrate, because a flat, rigid, and thermally-stable glass substrate can be used in the TFT fabrication process in our transfer technology. As a result, this technology realized an oxide TFT array for an AMOLED on a plastic substrate. Furthermore, in order to achieve a high-definition AMOLED, color filters were incorporated in the TFT array and a white organic light-emitting diode (OLED) was combined. One of the features of this device is that the whole body of the device can be bent freely because a source driver and a gate driver can be integrated on the substrate due to the high mobility of an oxide TFT. This feature means “true” flexibility.

We demonstrated the fabrication of a 200 nm×2 mm array of organic light-emitting diodes (OLEDs) on a glass substrate. The photolithographic technique using an optical phase shift mask allowed us to construct a super-fine resolution patterning of OLEDs. A single organic electroluminescent (EL) layer composed of an inert poly(methylmethacrylate) polymer binder and tetraphenylbendidine and tris(8-quinolinol) aluminum molecules was fabricated on a fine-resolution photoresist patterning by a spin coating method. The lines and spaces of the photoresist patterning were 200 nm. The emitting area was well confined by the regular array of residual photoresist resin walls. Finally, a MgAg cathode layer was uniformly deposited on the organic layer. We observed anisotropic EL spectra between the directions perpendicular and parallel to the patterning of OLED arrays. Furthermore, we observed a large difference of EL intensities between them. We assume that the anisotropic EL characteristics are caused by the confinement effect of photons inside the submicrometer-sized OLED array.

The Display Week 2021 Symposium Preview

In this paper, a novel digital camera sensor architecture to acquire images with high fidelity under low light conditions is proposed. Today, almost all digital cameras have only red, green, and blue color pixels. Due to their limited sensitivity to the wavelengths of visible light, the images captured using these color pixels under low light conditions are noisy. A new sensor architecture that has panchromatic pixels sensitive to all visible wavelengths along with the red, green, and blue pixels is proposed. Panchromatic pixels allow luminance information to be detected with higher sensitivity whereas red, green, and blue pixels produce the color information. Real images captured using the proposed sensor design are compared with the corresponding images obtained using a traditional digital camera having only red, green, and blue pixels. The results clearly show the feasibility of the proposed approach.

Electronic applications are continuously developing and taking new forms. Foldable, rollable, and wearable displays are applicable for human health care monitoring or robotics, and their operation relies on organic light-emitting diodes (OLEDs). Yet, the development of semiconducting materials with high mechanical flexibility has remained a challenge and restricted their use in unusual format electronics. This study presents a wearable full-color OLED display using a two-dimensional (2D) material-based backplane transistor. The 18-by-18 thin-film transistor array was fabricated on a thin MoS2 film that was transferred to Al2O3 (30 nm)/polyethylene terephthalate (6 μm). Red, green, and blue OLED pixels were deposited on the device surface. This 2D material offered excellent mechanical and electrical properties and proved to be capable of driving circuits for the control of OLED pixels. The ultrathin device substrate allowed for integration of the display on an unusual substrate, namely, a human hand.

Patterning organic light emitting diodes (OLEDs) with several micrometers resolution is of importance in applications such as micro displays, virtual and augmented reality devices. Here a fabrication method of micro OLEDs is reported, using conducting polymer polypyrrole (PPy) as nucleation layer. The photolithographically patterned PPy films are used for patterned growth of hole transport layer to locally confine carrier injection. High‐resolution red, green, and blue micro OLED arrays are demonstrated. The green micro OLEDs with stacked structure of Al/Alq3/NPB/PPy/ITO exhibit a maximum current efficiency of 3.41 cd A−1, which is 80% in comparison to those devices on indium tin oxide glass.

In this paper, we introduce the concept of building electronic sensate skins as extremely dense, multimodal, systolic sensor networks. In this fashion, the copious signals produced by the skin's receptors are reduced by the network itself, and only high-level features are routed out peer-to-peer, avoiding complex wiring requirements while promising to enable scalability across large areas. Our architectures and algorithms have been inspired by biological skin, where signals from receptors are enhanced or suppressed by processing in the receptor cells and nervous system before arriving at the brain. We illustrate this concept with work in progress on two test beds, the Pushpin Computer, an easily configurable, planar array of over 100 nodes set up as 'smart wallpaper', and the Tribble, a sphere coated with over 500 diverse tactile and noncontact sensor channels processed in 32 interconnected sensor 'cells'. We also introduce the Z-Tiles, a collaborative project that has resulted in a pressure-imaging floor realised through a collection of pixilated floor tiles configured as a mesh sensor network. We conclude with a technology roadmap for scaling to higher densities.

Liquid-crystal displays (LCDs) using thin-film transistor (TFT) arrays are particularly attractive because they have the potential for picture quality almost equal to that of CRTs. At present, the problem with TFT-LCDs is that the yield and throughput of the TFT fabrication process are economically low. Several recent papers have described methods for testing and repairing TFT arrays, The technique described in this paper uses optical charge sensing as a practical method for functional testing of TFT arrays. It is expected that manufacturers will be able to improve TFT-array yields and reduce costs by using this technique to determine the location and type of defects in arrays. The technique can also be used to characterize TFT arrays.

Thin Film Transistor (TFT) array technology is presented for Digital X-ray Sensors in Direct Radiography applications. Circuit simulations were performed to optimize the design of the TFT array. The sensor array uses a combination of a mushroom electrode with a high fill factor of 86% and a polymer passivation dielectric to minimize column capacitance and improve signal-to-noise ratio. A 14 in. X 8.5 in. sensor array with 1536 X 2560 pixels was developed using this technology. The TFT arrays are processed entirely in Class 1 clean room environments to eliminate line defects and minimize pixel defects. The best 14 in. X 8.5 in. panels have exhibited fewer than 0.001% pixel defects, as detected during in process testing prior to Se coating. In typical image quality comparisons with conventional X-ray film/screen combinations, the digital X-ray sensor exhibited equal or better performance than film-screens. Clinical studies were also conducted. Radiologists concluded that diagnostically significant projection radiographic images can be produced with the new digital X-ray sensor that are equivalent or superior to conventional film/screen images at the same X-ray exposures. The detector recently received FDA approval.

Mercuric iodide deposited on flat panel thin film transistor (TFT) array is one of the best alternate photoconductive materials for direct digital X-ray detectors for both static and moving image application in medical imaging. The mercuric iodide is coated onto the array by a Particle-In-Binder (PIB) process and scaled up to the 7inch 8.5inch size required in common medical imaging application. A TFT array with a pixel pitch of 139microns was used for detector. Mercuric iodide coating thickness around 200 microns was tested with beam energy between 40kVp and 100kVp utilizing exposure ranges typical for both static and dynamic imaging. Detector performances were evaluated by obtained images. Mercuric iodide deposited on flat panel thin film transistor (TFT) array is shown to exhibit high sensitivity to X-rays, excellent spatial resolution and high Detective Quantum Efficiency (DQE). Especially it is quite suitable for moving image because of low image lag. Resolution tests on resolution target phantoms showed that resolution is limited to the Nyquist frequency for the 139 microns (resolution ~3.6lp/mm) pixel detectors. The ability to operate at low voltages (~100V) gives adequate dark currents for most application and allows low voltage electronics designs. Also the detector can use exceptionally low dose-rate X-ray illumination because of the very high X-ray sensitivity, which exceeds any other known X-ray detector material. The fabricated detector represents the most advanced photoconductor material available today for flat panel, high resolution, x-ray, medical detector, which alternates conventional a-Se technology.

Top-emitting arrays of organic light-emitting diodes (OLEDs) have been fabricated and demonstrated on complementary metal–oxide–silicon (CMOS) circuitry. The 8×8 array of OLEDs is composed of 90 μm micropixels with a 55 μm separation. The OLEDs are based on an emitting layer of tris-(8-hydroxyquinoline)aluminum (Alq3) doped with coumarin 6 to provide green light emission. A layer of N,N′-diphenyl-N, N′-bis(3-methylphenyl)1-1′-biphenyl 1-4, 4′-diamine (TPD) was used as a hole transport layer and poly(ethylenedioxythiophene) doped with polystyrenesulfonate was used as a buffer layer between the TPD and the CMOS anode metal. Bright light was emitted through a semitransparent Mg:Ag cathode when the micropixel was driven by an individual current source.

The key to realizing completed bionic tactile perception of human skin using electronic skin relies on simultaneously distinguishing dynamic and static stimuli and restoring their characteristic information, which is realized by integration of several individual sensors but remains certain limitations including large physical size and high energy consumption. In this study, a piezoelectric-ultrasonic bimodal electronic skin (PUVE) based on in situ polarized PVDF-TrFE/2DBP composites and a thin-film transistor (TFT) array is fabricated. The incorporation of 2DBP into the PVDF-TrFE film and the in situ polarization approach provide excellent piezoelectric and ultrasonic performances of PVDF-TrFE/2DBP composites. PUVE has an ultrahigh sensitivity of 3.2 mV kPa-1 over a wide pressure (0-310 kPa) range, with excellent spatial resolution (50 μm) and response time (40 ms). Meanwhile, the PUVE demonstrated outstanding repeatability and bending stability in 1500 cycles of cyclic pressure and 4000 cycles of 180° bending. The integrated piezoelectric and ultrasonic functions of PUVE can respond individually to dynamic and static tactile stimuli to ensure perceiving and decoupling of the dynamical and static mechanical signals with one single sensor. The PVDF-TrFE/2DBP composites is further integrated with the TFT array, realizing visualization function of contacting objects and restoring their characteristic information including the texture and location. Thus, the PUVE is expected to have a wide range of applications in intelligent robots and human prostheses.

A 5 × 5 amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistor (TFT) array was successfully fabricated using a self-aligned imprint lithography (SAIL) process. This SAIL is a top-down process in which various TFT materials are pre-formed in multilayers and then unwanted areas are removed by plasma etching using a three-dimensional etch mask to fabricate the device. The fabrication of an a-IGZO TFT array using the SAIL process involves only a single imprint process followed by several successive plasma etching processes. Because SAIL does not require a photolithography process, there is no alignment error and uniform TFT arrays can be easily fabricated at a very high speed. The linear mobility of the 25 TFTs in the 5 × 5 a-IGZO TFT array fabricated using SAIL was 13.8 ± 1.53 cm2/V‧s at a gate voltage of 20 V. The average on/off ratio and threshold voltages were 3.92 × 106 and − 8.58 V, respectively, and showed uniform characteristics across 25 TFTs. The SAIL process, which does not require a photolithography process, is suitable for roll-to-roll processing using plastic substrates and can be used in the future to manufacture not only a-IGZO TFT arrays but also various other devices.