Oxide TFT Research Articles

16.1: Characteristics of Ln‐doped IZO TFT according to the Change of Indium concentration for DeMUX Applications

In order to narrow the bezel in high‐end IT and tablets, using switching circuit de‐multiplexer (DeMUX) reduces the number of source D/IC, making small LCD module available. In this study, new oxide TFT material, Ln‐doped InZnO (Ln‐IZO), has been developed. To achieve mobility of > 25cm2 /V.s, study focused on the effect of Indium (In) concentration on the fabrication of Ln‐IZO sputtering target, and fabricated the DeMUX‐equipped 14 inch FHD driven by gate on array (GOA).

New Structure of High Current Driving Oxide TFT for Ultra-High Resolution Display

New Structure of High Current Driving Oxide TFT for Ultra-High Resolution Display

A New Pixel Circuit Compensating for a Decrease in Luminance of the Stretchable Active Matrix Organic Light Emitting Diode Display

The stretchable display is a next-generation flexible display because it is possible to implement free-form with free change, and various studies are being conducted. The most likely display technology for implementing a stretchable display is the organic light emitting diode (OLED), which is suitable for forming on flexible substrates because it can emit light on its own without using the back light unit (BLU). In addition, through advantages such as high contrast ratio, fast response time, and wide viewing angle, OLED is applied from small size panels such as mobile to large size panels such as televisions. Thin film transistor, a device applied to drive active matrix of OLED, is represented by the amorphous silicon (a-Si), low temperature poly silicon (LTPS), and oxide TFT such as amorphous In-Ga-Zn-oxide(a-IGZO). The a-IGZO, which has advantages such as high filed effect mobility and low leakage current compared to a-Si:H, is used as a backplane of commercial OLED panels. In addition, it is suitable for application to flexible substrates due to low process temperature, and high transmittance in the visible area due to band gap energy of about 3.1 eV can be applied to transparent display. In research to minimize damage to TFTs or OLEDs when the area of flexible substrates increases, rigid island structures protect devices from damage by forming rigid structures on soft substrates. Devices protected from damage caused by increasing the area can maintain performance, and each pixel can maintain brightness. However, when the area of the panel is increasing, the gap between the pixels increases, which leads to a decrease in the luminance of the panel. Among the studies to compensate for the decrease in brightness by increasing the area of the stretchable display, Kang et al. proposed a stretchable pixel circuit for AMOLED displays, which compensates for the reduced luminance by bootstrapping. The proposed circuit increases luminance through a variable capacitor with a strain-dependent capacity change. However, compensation for TFT's threshold voltage and voltage drop, which are possible causes of luminance reduction in OLED were not considered. The threshold voltage or power voltage of a different drive TFT for each pixel affects the current supplied from the backplane to the OLED electrode, and the current supplied differently for each pixel affects the light intensity of the OLED device, so compensation should be considered. In this study, we propose a novel pixel circuit consisting of seven n-type transistors and two capacitors. In order to evaluate the compensation ability of the proposed pixel circuit, a simulation using the RPI Level = 35 model was conducted. Fig. 1 (a) shows the simulation result of the output current of the proposed pixel circuit by the change in the capacitance of C2. Before the capacitance of C2 increased, the output current was 7.65 μA, but when the capacitance of C2 increased by 10%, the output current increased by 2.22% to 7.82 μA, and when the capacitance of C2 increased by 4.31%.Figure 2 (b) shows the output current caused by the change in VDD voltage of the proposed pixel circuit and the conventional pixel circuit. As the VDD of the conventional pixel circuit changed by 3.0 V, the output current decreased by 40.90% from 8.02 μA to 4.74 μA. In the case of proposed pixel circuit, output current decreased by 21.83% from 7.65 μA to 5.98 μA as VDD changed by 3 V, and decreased by 0.77% to 7.60 μA when VDD changed by 1.1 V. Figure 3 shows the output current due to the threshold voltage change of TFT in the proposed pixel circuit and conventional pixel circuit. In the conventional pixel circuit, output current changed from 10.13 μA to 5.53 μA as the threshold voltage of TFT changed by 3 V. In the proposed pixel circuit, output current changed from 7.12 μA to 6.45 μA with a 3 V change in the threshold voltage. As a result of the simulation, the proposed pixel circuit can compensate for luminance change by an increased area, voltage drop, and the threshold voltage shift of the TFT. Figure 1

(Invited) Challenging for High-Performance Oxide-TFT Based Inverters

Metal oxide-Thin-film transistor (oxide-TFT)-based inverter circuit is a critical technology for the development of next-generation cost-effective ubiquitous device applications for wearable information and healthcare technology. However, in contrast to the success of n-channel oxide-TFT that already implemented in state-of-art high-performance flat-panel-displays, the development of oxide-inverter technology, especially p-channel oxide-TFT, still remains the largest challenging in oxide-TFT technology. The absence of reliable high-performance oxide-TFT inverter is mainly attributed to the insufficient device performances of p-channel oxide-TFTs, and especially large off-current causes large device power-consumption. Therefore, developing p-channel oxide-TFT exhibiting a low off-current and sharp s-value is indispensable for low-power operational oxide-inverter circuits.This talk discuss how we improve p-channel oxide TFT performance for oxide-TFT-based inverters. After we review the recent progress of oxide-TFT-based inverter and p-channel oxide-TFTs, we identify the current issues and the remaining challenging for oxide-inverters.To improve the device performances of p-channel oxide-TFT such as SnO-TFT, I present an atomically-ultra-thin oxide channel technology, which offers several advantages such as effective gate control of a conductive metal oxide channel in full-carrier depletion operation mode. This is a promising to improve the devcie performances for several oxide-TFTs having a high carrier-doped oxide channel. To the end, we discuss the device characteristics for oxide-TFT-based-inverter for the ultra-thin oxide-TFT-based CMOS and NMOS inverters.

12.2: High Performance AMOLED Pixel Circuit Using Interleaved Emit Signals Based on Low‐Temperature Poly‐Si and Oxide (LTPO) TFTs

A concise pixel circuit with interleaved Emit signals is proposed for active matrix organic light‐emitting diode (AMOLED) displays, on the basis of low‐temperature polycrystalline silicon oxide (LTPO) TFTs. The oxide TFT can be re‐used for both initialization and threshold voltage extraction periods, using interleaved Emit signals of adjacent lines with overlapped waveforms. The proposed pixel circuit consists of 1 oxide TFT and 5 p‐type LTPS TFTs, while only 2~3 types of line‐by‐line scanning driving signals, i.e. the Emit signal and the Scan signal, are required. Implementation of the proposed pixel circuit shows that the occupation can be reduced to 40 μm × 56.7 μm. Furthermore, optimization of the pixel circuit shows the emission current error is less than 2.3% with threshold voltage variation of ± 0.5 V, while refresh rate from 1 to 120 Hz can achieved.

Mixed-Signal Building Blocks for Communication Systems Using Flexible Oxide TFT Technology

This article reports two important mixed-signal building blocks using unipolar oxide thin-film transistors (TFTs) on a 30- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick polymide substrate, which find potential application in communication systems. These blocks include a low-voltage bootstrapped (BS) switch and a latch-type comparator designed using a device channel length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu \text{m}$ </tex-math></inline-formula> . Functional demonstration of these blocks has been carried out from measurements under normal ambient conditions with a load of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}\Omega ||12$ </tex-math></inline-formula> pF at a supply voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {DD}}$ </tex-math></inline-formula> ) not exceeding 3 V. While the BS switch shows a linear ON-resistance of 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> , at a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {DD}}$ </tex-math></inline-formula> of 2 V, without any voltage drop across it, the proposed comparator has shown a very low offset of 10 mV with a decision time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4~\mu \text{s}$ </tex-math></inline-formula> . These blocks help in expanding the application of oxide TFT technology in communication systems to design the binary amplitude-shift keying (BASK) modulator and demodulator circuits.

48.3: Variable Top Gate Oxide TFT Structures for Premium High‐end Display with Process Simplicity and Device Stability

48.3: Variable Top Gate Oxide TFT Structures for Premium High‐end Display with Process Simplicity and Device Stability

(Invited) Oxide TFT Applications: Principles and Challenges

Oxide thin film transistors are emerging devices in high-speed, low- power active matrix displays. There are many other applications of this kind of device. The author analyzed these applications and categorized TFTs into three functions: as a control or readout unit for the attached device, as a switching device in circuits, and as a functional element itself in sensors. Examples on each function are shown and discussed. Future applications and challenges on oxide TFTs are presented.

Effect of oxygen defect on the performance of Nd: InZnO high mobility thin-film transistors

High mobility and stability are eternal themes for oxide semiconductor TFT. However, there is a natural contradiction between mobility and stability. The oxygen defect state has a great influence on oxide semiconductor devices, so we adopt different sputtering oxygen percentages to prepare Nd: InZnO films of different deposition states. The type and number of oxygen defects were extracted and fitted by μ-PCD, XPS, and CV. Through a series of characterization tests on thin films and devices, the influence mechanism of oxygen-related defect states on the performance and instability of high mobility oxide TFT was analyzed. The results show that the stability of TFT can be improved by appropriately increasing the oxygen percentage, but some mobility will be lost. Finally, we have achieved devices with high mobility and good stability by cleverly designing homojunction TFT. The best device performance is μsat=38.2 cm2V–1S–1, SS= 0.13 V/dec, Vth≈ 0 V, Ion/off= 4.3 × 108. This is a simple and effective way to prepare high-performance TFT circuits.

P‐19: Performance Development of Oxide Semiconductor Photodiode with High Work Function Electrode Suitable for Mass Production

IGZO as the typical representative of oxide semiconductor used for TFT devices, has been widely used in display panel foundary, such as large size OLED, LTPO technology direction. To develop oxide based photodetector (sensor), not only can expand the application direction of oxide semiconductor material, moreover the oxide photodetector integrated with oxide TFT is more convenient. We developed several oxide based vertical MSM photodiode with schottky junction, the IGZO MSM can respond to ultra violet(UV), while new oxide material S1 and S2 can response to blue light. In order to form a schottky junction, metal electrodes materials should have high work function, thus we developed a high work function electrode suitable for mass production, and of witch work function is ~4.7eV. In addition, in order to gain the characteristics of diode, the ACT film need be deposited in high oxygen process to prevent form ohm contact. Assisted by TCAD simulation, we researched how to control the oxide schottky junction, including schottky junction, barrier tunneling, to instruct the material selection and electrical properties of control.

15‐1: Novel Multi‐Frequency Driving of OLED for Low Power Consumption

In a recent, OLED display has been required to larger and higher resolution by the years. So, display image quality and power consumption are getting important. It is necessary to reduce power consumption to increase battery usage time. Low frequency driving is the significant factor for long‐term use. We can operate low frequency driving using oxide TFT with small leakage current. However, the low frequency driving operates when the entire screen is a still image. To improve power consumption, we propose Multi‐Frequency Driving (MFD) technology. MFD is a technology that divides moving and still image areas in full screen display and drives them at different frame frequency. In this paper, we suggest what MFD technology is and how to implement the OLED driving system. And then we show how much it can improve power consumption for OLED.

74‐1: 31″ Flexible Printed OLED TV Display Technology: It's TV Mobiles

The flexible printed OLED TV display technology will be able to create new application market, such as rollable/foldable TV, in the future. It's TV Mobiles. Recently, the TCL (Guangdong Juhua Printed Display Technology Ltd. Co, TCL CSOT &amp; TCL Corporate Research) has successfully demonstrated the 31″ FHD flexible printed OLED TV in CES 2020. The product is fabricated by ink jet printing technology with top emission OLED device architecture, advanced encapsulation technology and is driven by IGZO oxide TFT B/P technology. The panel performance of 31″ flexible printed OLED TV has continuously improved drastically after demonstration at CES based on optimization of top emission OLED device architecture including printing OLED material development, MURA free printing technology, Oxide TFT B/P technology and advanced thin film encapsulation technology. The RGB device performance of 31” FHD flexible printed OLED TV has high current efficiency and long‐life time,R:(0.68,0.32), 46.3cd/A, LT95&gt;8khrs@1knits,G:(0.28,0.70),115.5cd/A, LT95&gt;6khrs@1knits,B:(0.13,0.062),5.35cd/A, LT95 &gt;0.35khrs@1knits respectively.It is getting closer and closer to meet the commercial requirement of flexible OLED TV target specification. The technical challenges of 31″ FHD flexible printed OLED TV are also identified. In this paper, the technology development status and technical challenges are discussed

P‐117: AI Analysis of HOP Circuit Failure and Improvement

AMOLED's HOP(hybrid of Oxide semiconductor and Polysilicon TFT) technology was born to meet the market's demand for low power consumption. Also, the IGZO oxide process was introduced with new driving technology to support the low driving frequency operation. However, this new GC circuit of oxide TFT driving caused new and randomly appearing horizontal defects which do not exist in LTPS circuits. To solve this issue, we studied to find the design parameters using pipelined deep learning models composed of CGAN(Conditional Generative Adversarial Network), VGM(Variational Gaussian Mixture), and XAI(eXplainable Artificial intelligence) technologies to figure out what causes these defects. We collected HOP panel design information to achieve the given goal and confirmed the degree of defect per HOP model. Since the number of HOP models is limited, XAI analysis might also be negligible. We solve this issue by generating data using CGAN and VGM in sequence. After, ALE(Accumulated Local Effects), a popular XAI technique, is applied to find affected design parameters and change‐related circuit designs to help verify the proposed algorithm's performance. As a result of this design change, we identified that the related defect rate decreases from 15000ppm to less than 500 ppm, in which XAI plays a significant role in solving a newly introduced defect issue. That was believed for a long time a challenging problem to analyze using the legacy SPICE tool in the OLED circuit field. Our result also suggests that even predicting the defect rate of future HOP models becomes feasible with our proposed deep learning architecture.

Preview the Products on Display at Display Week 2022

Preview the Products on Display at Display Week 2022

Physical parameters based analytical I-V model of long and short channel a-IGZO TFTs

This paper presents an analytical model for amorphous In-Ga-Zn-O thin film transistors based on device physics. The proposed model comprises physical parameters including subgap density-of-states (DOS) and is useful for fabrication process optimization. In addition to delocalized free band states, the model accounts for deep and tail trap states and is valid for complete region of operation. Physical parameters are extracted by employing least square (LSQ) curve-fit function and the model is validated by comparing model outcome with measured characteristics of the device. The proposed model is able to predict the I-V characteristics of the long channel devices to good accuracy. Further, this model is enhanced to predict the behavior of the short channel devices by taking contact voltage drop into account. The model accurately reproduces the measured response of long and short channel oxide TFTs with channel length ranging from 20 μm down to 2 μm with channel width fixed to 20 μm. The average error between measured data and model outcome is found to be < 3 %. The proposed model is useful to design oxide TFT based circuits with different channel lengths using a single set of physical parameters through circuit simulator.

A modulus-engineered multi-layer polymer film with mechanical robustness for the application to highly deformable substrate platform in stretchable electronics

Mechanical robustness and deformability of substrate platforms are essential for high-performance stretchable electronics. However, there are still challenges because of rigid island design for device protecting that induces large modulus mismatch and impedes the out-of-plane deformation. Herein, a substrate platform with superb mechanical durability and deformability is newly devised by introducing a multi-layer polymer film (MLPF), where the modulus of each layer was engineered precisely range from 105 to 109 Pa. The modulus-engineered MLPF was integrated monolithically onto various elastomer substrates via sequential film deposition using initiated chemical vapor deposition (iCVD). The developed substrate platform exhibited outstanding robustness against various modes of deformations. Especially the tensile deformation, MLPF structure enhanced mechanical durability by 102 times than a single-layer island structure while keeping the strain on the island below 1 % even with the 99 % of global strain. The developed substrate platform was applied for amorphous Indium-Gallium-Zinc oxide TFT array. The TFT performances were maintained even under 30 % of tensile strain and they were fully retained after 105 times of repeated tensile deformation. The newly suggested substrate platform and design rule of MLPF structure will serve as a guideline for integration of future stretchable/wearable electronics achieving superb mechanical robustness and long-term operation.

Mobility Enhancement in P-Type SnO Thin-Film Transistors via Ni Incorporation by Co-Sputtering

Oxide semiconductors have been considered one of the most promising candidates for flexible electronics applications owing to their low process temperatures and good reliability. However, the low mobility of p-type oxide semiconductors limits the performance of flexible oxide-TFT-based CMOS technology. In this study, p-type SnO_<i>x</i>:Ni thin films were deposited by reactive rf magnetron co-sputtering, a technique compatible with the current industrial semiconductor manufacturing technology, from Sn and Ni targets. As the Ni-gun power increased, the distribution of Ni in the SnO_<i>x</i>:Ni thin film changed from a more uniform dispersion to nanoclusters, resulting in the crystalline phase transition of SnO_<i>x</i>:Ni from <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-SnO (110)-dominant polycrystalline to amorphous and then to <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-SnO (101)-dominant polycrystalline. A high-mobility inverted-staggered p-type SnO_<i>x</i>:Ni TFT was then fabricated on a glass substrate with a maximum process temperature of 225&#x00B0;C, which is compatible with flexible polymeric substrates. The TFT fabricated at an optimal Ni-gun power of 42 W exhibited an impressive field-effect mobility of 11 cm²V^&#x2212;1s^&#x2212;1 and on current of <inline-formula> <tex-math notation="LaTeX">$35.2 ~\mu \text{A}$ </tex-math></inline-formula> per channel width-to-length ratio; these values are comparable to those of a typical n-type oxide TFT. These results should contribute toward flexible oxide-TFT-based CMOS technology.

Paper] Improvement of Internal Compensation by Differential Offset Method for OLED Display Using High Mobility Oxide TFT

Paper] Improvement of Internal Compensation by Differential Offset Method for OLED Display Using High Mobility Oxide TFT

A Pulse Width Modulator Using a High-Speed Comparator With Flexible Oxide TFT Technology

A Pulse Width Modulator Using a High-Speed Comparator With Flexible Oxide TFT Technology

Investigation of NBIS Degradation Mechanism in Oxide TFT Assisted by Charge Trap Phenomena

Investigation of NBIS Degradation Mechanism in Oxide TFT Assisted by Charge Trap Phenomena