igzo tft display manufacturer

Indium gallium zinc oxide (IGZO) is a semiconducting material, consisting of indium (In), gallium (Ga), zinc (Zn) and oxygen (O). IGZO thin-film transistors (TFT) are used in the TFT backplane of flat-panel displays (FPDs). IGZO-TFT was developed by Hideo Hosono"s group at Tokyo Institute of Technology and Japan Science and Technology Agency (JST) in 2003 (crystalline IGZO-TFT)electron mobility of amorphous silicon, which has often been used in liquid-crystal displays (LCDs) and e-papers. As a result, IGZO-TFT can improve the speed, resolution and size of flat-panel displays. It is currently used as the thin-film transistors for use in organic light-emitting diode (OLED) TV displays.

In 2012, Sharp was first to start production of LCD panels incorporating IGZO-TFT.smartphones, tablets, and 32" LCDs. In these, the aperture ratio of the LCD is improved by up to 20%. Power consumption is improved by LCD idling stop technology, which is possible due to the high mobility and low off current of IGZO-TFT.pixel-density panels for notebook applications.LCD of an ultrabook PC supplied by Fujitsu,Razer Blade 14" (Touchscreen Variant) Gaming Laptop and a 55" OLED TV supplied by LG Electronics.

IGZO"s advantage over zinc oxide is that it can be deposited as a uniform amorphous phase while retaining the high carrier mobility common to oxide semiconductors.transistors are slightly photo-sensitive, but the effect becomes significant only in the deep violet to ultra-violet (photon energy above 3 eV) range, offering the possibility of a fully transparent transistor.

The current impediment to large-scale IGZO manufacturing is the synthesis method. The most widely used technique for Transparent Conducting Oxide (TCO) synthesis is Pulsed Laser Deposition(PLD).laser is used to focus on nano-sized spots on solid elemental targets. Laser pulse frequencies are varied between the targets in ratios to control the composition of the film. IGZO can be deposited onto substrates such as quartz, single-crystal silicon, or even plastic due to its ability for low-temperature deposition. The substrates are placed in a PLD vacuum chamber, which controls oxygen pressure in order to ensure favorable electrical properties. After synthesis, the film is annealed, or gradually exposed to air to adjust to the atmosphere.

Liquid crystal displays (LCD) began to replace cathode-ray tube-based televisions in the early 2000s. The pixels in these LCDs were, until 2012, driven exclusively by thin-film transistors (TFTs) that use amorphous hydrogenated silicon (a-Si:H) as the semiconducting channel. But as demand grew for ever larger displays, with better viewing and energy performance, a need for improved TFTs emerged. TFTs block light coming from the display, so they need to be small, which lowers their current-driving ability. Additionally, there was a push to move away from LCD technology and into organic light emitting diodes (OLEDs) in order to capitalize on their better performance, which includes direct emission and richer colours, but OLEDs need to be driven by large amounts of current, at levels a-Si:H TFTs cannot accommodate. What was needed was a new technology that could be used to create TFTs with a high charge carrier mobility, which could drive large currents.

Charge carrier mobility tells us how quickly charge carriers (electrons and holes) can move through a semiconductor, and determines the amount of current we can drive through a TFT of a given size. This is limited by the nature of the path that charge carriers take though a material. This path can be thought of in terms of the atomic orbitals and how they interconnect to make up the conduction and valence bands — the energetic levels at which the electrons and holes are free to move around. The sp3 hybridized orbitals in silicon are highly directional, and in the crystalline state the silicon–silicon bonds properly overlap, providing an efficient path to travel through. However, in amorphous silicon, structural disorder leads to disconnects and conduction cannot occur through the orbitals in the same way. Instead, the charge carriers have to hop across the orbitals, which leads to mobilities of at most 1 cm2 V–1 s–1 — about 2–3 orders of magnitude lower than in crystalline silicon.

After a few years verifying the validity of the hypothesis, we started research on transparent oxide TFTs. To develop high-mobility TFTs using transparent conductive oxides, the major issue was their high carrier concentrations (the TFTs can’t be turned off). Indium oxide is a typical transparent conductive oxide with a large mobility, but reducing its excessive carrier concentration is difficult due the ease with which oxygen vacancies form. We tested InGaO3(ZnO)m epitaxial films, where m = 4 and 5, as I believed the unique local structure around Ga3+ would help lower the carrier concentration. As expected, the carrier concentration in epitaxial InGaO3(ZnO)4 reduced to a suitable level, and when applied in TFTs showed excellent performance, with a mobility of approximately 80 cm2 V–1 s–1. We then fabricated thin films using amorphous InGaZnO4 (a-IGZO). The electron concentrations in the resulting a-IGZO thin films, which were deposited on glass substrates at room temperature, were below 1016 cm–3 and the TFTs exhibited mobilities of approximately 10 cm2 V–1 s–1 — an order of magnitude larger than that of a-Si:H TFTs. We also found that TFTs fabricated on plastic substrates offered almost identical performance (Fig. 1). At this point we applied for patents and then submitted our paper to Nature, which was published in 2004.

Demonstrations of IGZO TFT-based displays began to emerge in 2007, when Samsung Electronics first reported a-IGZO TFT-based high-definition LCDs. Demonstrations of IGZO TFT-based backplane LCDs in smart phones and tablet computers then appeared around 2012. Arguably the most striking application emerged in 2015, when LG Display demonstrated large-sized OLED televisions. Here the a-IGZO TFT was indispensable because of the need for high mobility and simple formation over large areas.

I believe the success of IGZO transistors is due to a number of factors. First is their high mobility, which is an order of magnitude higher than a-Si:H, and the excellent controllability of their carrier concentration. Second, the production process is almost the same as a-Si:H, except for the deposition of the channel layer (chemical vapour deposition is used for a-Si:H whereas sputtering is used for IGZO), making integration into current manufacturing workflows relatively painless. Third, synthesizing large-sized high-quality sputtering targets is relatively easy, which also makes thin-film deposition on large-sized substrates a relatively simple task. With these attributes, IGZO transistors provide a promising backplane technology to drive the future of flat panel displays.

The thin-film transistor (TFT) became commercially available slightly more than 30 years ago in the form of a switch for the Liquid Crystal Display. It all started with an amorphous silicon (a-Si) TFT. Compared to the traditional crystalline silicon CMOS transistor, the a-Si TFT can be produced on large substrates and at low processing temperatures, below 300 °C, enabling integration on glass substrates and even flexible substrates.

A-Si TFTs are mainly implemented as simple pixel switches due to their low charge carrier mobility (0.5-1 cm²/Vs). An alternative semiconductor on glass substrates is low-temperature polycrystalline silicon (LTPS), outperforming a-Si TFTs by a 100x larger mobility (50-100 cm²/Vs) and often used for high-end displays and imagers. Despite the advantages, fabrication of an LTPS TFT takes more process steps, is limited in substrate size, and requires a larger process temperature. Oxide-based semiconductors as indium-gallium-zinc-oxide (IGZO) fill this gap between a-Si and LTPS nicely, exhibiting low processing temperatures and a decent charge carrier mobility of 10 up to 40 cm²/Vs [1].

Figure 1: Example cross-section of an IGZO TFT with a dual-gate fabricated on a glass substrate. The top and bottom gates can be connected by vias through the first metal layer (M1). Silicon dioxide (SiO2) is used to insulate the gates from the active IGZO layer, to achieve the field-effect transistor. After fabrication, the glass can be detached from the polyimide layer resulting in a flexible circuit.

With such characteristics, the IGZO TFTs can be used to fabricate relatively complex circuits on flexible substrates. Consequently, IGZO TFTs are evolving beyond displays and entering the fields of wearable devices and the Internet of Things (IoT). Some highlights include an ultra-flexible circuit for recording electrocardiograms [2], radiofrequency identification (RFID) tags and near-field communication (NFC) tags [1]. Even the memory field has noticed IGZO and its extremely low OFF current and recently demonstrated a capacitor-less IGZO-based DRAM cell with a retention time longer than 400 seconds [3]. We can expect the first IGZO products beyond display applications to emerge in the near future.

As with a large majority of products, electrostatic discharge (ESD) protection is an important concern. If we are to see IGZO products enter the fields of IoT or biomedical engineering, they will have to include ESD protection.

Perhaps ESD protection is not a great concern for wireless products, for example, NFC and RFID tags which have no wired input and output ports. Here the sensitive electronic parts will not be exposed to the user as they are electrically insulated. In this case, like for displays [4,5], a good ESD control program might be enough to protect the IGZO components during assembly. The full display will, in any case, include ESD protection circuits at the system level, even perhaps at the peripherals where the electrical connections leave the display, but not necessarily at the IGZO component level. On the other hand, some wearables like the electrocardiogram patch, might not be able to affordsystem-level ESD protection circuits fabricated in a different technology other than IGZO. Since the electrodes have direct contact with the end-user, they may require ESD protection circuits at the device level. The same will be true for displays and imagers if their peripheral circuits are implemented using IGZO – to enable a fully flexible display, for example.

Yes, like any digital or analog circuit, also IGZO TFT circuits are susceptible to ESD. Even though the IGZO TFT technology nominal voltage can be as high as 10 V, degradation and breakdown can be observed already at 20 to 30 V [6]. To avoid damage to performance, the IGZO circuit should never be exposed to voltages higher than 20 V. This means the eventual ESD protection circuits should have a clamping voltage lower than 20V, which is only twice the nominal voltage. These limits depend on the IGZO technology and could change as the technology improves.

There are several challenges when designing IGZO TFT circuits in general, but perhaps the most prominent one is the fact it is a unipolar technology. Unlike the complementary metal-oxide-semiconductor (CMOS) technology integrating two types of transistors, n-type and p-type, the IGZO TFT only provides n-type transistors. Research on p-type oxide-based TFTs to complement the IGZO n-type transistor exists. Unfortunately, the p-type transistors generally have a much lower charge carrier mobility and would make the complementary design less efficient than the unipolar one [1]. Since ESD protection circuits can rarely dictate the technology evolution, ESD protection designs will most likely have to be made with unipolar circuits too.

The second challenge of the IGZO TFT technology for ESD circuit design is that there are usually no diodes available. Even though it is possible to make diodes in the IGZO TFT technology, it also increases the process cost and is not a commodity in this industry. Therefore, the best next choice would be a diode-connected transistor. The technology options to improve the ESD performance of the diode-connected transistor would be to smartly use the back-gate or to optimize the channel material resulting in larger mobility.

Luckily, the negative threshold issue that was observed in the early IGZO TFT technology improved significantly. Therefore, the significant leakage at the zero-volt bias that would be present in IGZO TFT ESD protection circuits can be solved from the technology side.

Figure 3: Drain-to-source current as function of the gate-to-source voltage measured on a dual-gate IGZO transistor shows a positive threshold voltage (top) and leakage currents below the measurement setup noise level (bottom). These data have been measured on a 5 µm by 100 µm TFT with a drain-to-source bias voltage of 50 mV.

Nevertheless, given the limited IGZO TFT conductivity, to achieve a product-worthy ESD protection level, the ESD circuits will have to be in the millimeter or even centimeter size range [5][2]. Given the IGZO TFT technology is optimized for large areas, spending these kinds of areas for ESD protection should not be a showstopper.

Unlike the silicon integrated circuit technology, there is a very limited choice of devices in IGZO, which also limits the possible solutions of ESD protection circuits. Passive devices could help with that. Inductors, capacitors, and resistors could be used as ESD protection or to complement the active devices. A spark gap could be a compact ESD protection option too.

IGZO TFT technology is a good candidate for future wearable and flexible electronic devices. If it is used in a wireless or non-contact way, consumer-side ESD protection should not be a great concern. However, if it will be used as a wearable with electrically exposed pads, it will certainly require ESD protection designs and ESD testing. In this case, the ESD testers might need to be adapted. Take the Human Body Model (HBM) ESD tester, for example. Most HBM ESD testers today target small, packaged devices in millimeter or centimeter sizes. HBM ESD testing of an IGZO TFT product might imply pins to be more than 10 cm apart. That might be challenging indeed, but perhaps some ingenious test fixtures or packaging could overcome this. Bending the flexible wearable device for ESD testing purposes could be an example.

The Transmission Line Pulse (TLP) ESD tester could be an alternative to HBM testing. Since the TLP tester is of a more academic nature than the HBM tester, it could perhaps offer more flexibility in connecting to the large IGZO circuit. Even though the TLP is a 50-Ohm tester while HBM has a typical series resistance of 1500 Ohm, we have observed comparable ESD testing results with both testers [6]. Since there is no universal conversion rule, care needs to be taken when interpreting TLP measurement results as HBM protection values.

An IGZO display is any display panel that uses indium gallium zinc oxide or IGZO as the primary semiconducting material in its thin-film transistor or TFT. Hence, it is not a display technology but rather, a specific backplane technology for driving and addressing transmissive or emissive components of a particular panel.

Some of the notable examples of a display technology include LCD technologies such as in-plane switching or IPS LCD and twisted nematic or TN LCD, as well as organic light-emitting diode or OLED technology, and microLED technology. On the other hand, there are three major backplane technologies: IGZO TFT, amorphous silicon or a-Si TFT, and low-temperature polysilicon or LTPS TFT.

• Note that a-Si-TFT is not transparent but can be stretched thin enough to allow an adequate amount of light to pass through. An IGZO-TFT is naturally transparent, thus translating to specific advantages such as brighter display panels and energy efficiency, reduced need for backlighting in the case of LCDs, and reduced brightness output in OLED and LED displays.

• Another advantage of IGZO display is that it has 30 to 50 times more electron mobility than a-Si display. Better electron flow means higher resolutions and faster pixel response time to allow the manufacturing of smaller panels with high pixel density. Earlier prototypes using indium gallium zinc oxide featured a 6-inch panel at 2560×1600 pixels or 498 pixels per inch.

• Note that transparency and better electron mobility also mean that these displays are more power-efficient than those based on amorphous silicon. Furthermore, it has a lower leakage current than both amorphous and low-temperature polysilicon TFT, thus allowing it to retain an active pixel state longer, especially when displaying still images such as photographs and documents.

• Manufacturing IGZO displays also require the use of rare-earth materials. More specifically, indium and gallium are rare. They are costly to extract from their point of origin and procure from the suppliers. This drawback introduces cost and supply risks for manufacturers of display panels and consumer electronic devices.

• Another disadvantage is that producing displays based on this semiconductor is more complicated than manufacturing a-Si TFT display panels. The current challenge to mass-producing indium gallium zinc oxide is the relevant synthesis method using Pulsed Laser Deposition or PLD. However, PLD requires expensive equipment and lengthier time. These requirements can hamper large-scale production.

• It is also worth mentioning that LTPS displays have key advantages over IGZO displays and a-Si displays. More specifically, it has better and faster electron flow, allows the production of small-sized screens with high pixel density, and more efficient power consumption.

Miyata, Y., Furuta, M., Yoshioka, T., and Kawamura, T. 1992. “Low-Temperature Polycrystalline Silicon Thin-Film Transistors for Large-Area Liquid Crystal Display.” Japanese Journal of Applied Physics. 31(P. 1, No. 12B): 4559-4562. DOI: 1143/jjap.31.4559

LCD or AMOLED, 1080p vs 2K? There are plenty of contentious topics when it comes to smartphone displays, which all have an impact on the day to day usage of our smartphones. However, one important topic which is often overlooked during analysis and discussion is the type of backplane technology used in the display.

Display makers often throw around terms like A-Si, IGZO, or LTPS. But what do these acronyms actually mean and what’s the impact of backplane technology on user experience? What about future developments?

For clarification, backplane technology describes the materials and assembly designs used for the thin film transistors which drive the main display. In other words, it is the backplane that contains an array of transistors which are responsible for turning the individual pixels on and off, acting therefore as a determining factor when it comes to display resolution, refresh rate, and power consumption.

Examples of backplane technology include amorphous silicon (aSi), low-temperature polycrystalline silicon (LTPS) and indium gallium zinc oxide (IGZO), whilst LCD and OLED are examples of light emitting material types. Some of the different backplane technologies can be used with different display types, so IGZO can be used with either LCD or OLED displays, albeit that some backplanes are more suitable than others.

Amorphous silicon has been the go-to material for backplane technology for many years, and comes in a variety of different manufacturing methods, to improve its energy efficiency, refresh speeds, and the display’s viewing angle. Today, a-Si displays make up somewhere between 20 and 25 percent of the smartphone display market.

For mobile phone displays with a pixel density lower than 300 pixels per inch, this technology remains the preferable backplane of choice, mainly due to its low costs and relatively simple manufacturing process. However, when it comes to higher resolution displays and new technologies such as AMOLED, a-Si is beginning to struggle.

AMOLED puts more electrical stress on the transistors compared with LCD, and therefore favours technologies that can offer more current to each pixel. Also, AMOLED pixel transistors take up more space compared with LCDs, blocking more light emissions for AMOLED displays, making a-Si rather unsuitable. As a result, new technologies and manufacturing processes have been developed to meet the increasing demands made of display panels over recent years.

LTPS currently sits as the high-bar of backplane manufacturing, and can be spotted behind most of the high end LCD and AMOLED displays found in today’s smartphones.  It is based on a similar technology to a-Si, but a higher process temperature is used to manufacture LTPS, resulting in a material with improved electrical properties.

LTPS is in fact the only technology that really works for AMOLED right now, due to the higher amount of current required by this type of display technology. LTPS also has higher electron mobility, which, as the name suggests, is an indication of how quickly/easily an electron can move through the transistor, with up to 100 times greater mobility than a-Si.

For starters, this allows for much faster switching display panels. The other big benefit of this high mobility is that the transistor size can be shrunk down, whilst still providing the necessary power for most displays. This reduced size can either be put towards energy efficiencies and reduced power consumption, or can be used to squeeze more transistors in side by side, allow for much greater resolution displays. Both of these aspects are becoming increasingly important as smartphones begin to move beyond 1080p, meaning that LTPS is likely to remain a key technology for the foreseeable future.

The drawback of LTPS TFT comes from its increasingly complicated manufacturing process and material costs, which makes the technology more expensive to produce, especially as resolutions continue to increase. As an example, a 1080p LCD based on this technology panel costs roughly 14 percent more than a-Si TFT LCD. However, LTPS’s enhanced qualities still mean that it remains the preferred technology for higher resolution displays.

Currently, a-Si and LTPS LCD displays make up the largest combined percentage of the smartphone display market. However, IGZO is anticipated as the next technology of choice for mobile displays. Sharp originally began production of its IGZO-TFT LCD panels back in 2012, and has been employing its design in smartphones, tablets and TVs since then. The company has also recent shown off examples of non-rectangular shaped displays based on IGZO. Sharp isn’t the only player in this field — LG and Samsung are both interested in the technology as well.

The area where IGZO, and other technologies, have often struggled is when it comes to implementations with OLED. ASi has proven rather unsuitable to drive OLED displays, with LTPS providing good performance, but at increasing expense as display size and pixel densities increase. The OLED industry is on the hunt for a technology which combines the low cost and scalability of a-Si with the high performance and stability of LTPS, which is where IGZO comes in.

Why should the industry make the switch over to IGZO? Well, the technology has quite a lot of potential, especially for mobile devices. IGZO’s build materials allow for a decent level of electron mobility, offering 20 to 50 times the electron mobility of amorphous silicon (a-Si), although this isn’t quite as high as LTPS, which leaves you with quite a few design possibilities. IGZO displays can therefore by shrunk down to smaller transistor sizes, resulting in lower power consumption, which provides the added benefit of making the IGZO layer less visible than other types. That means you can run the display at a lower brightness to achieve the same output, reducing power consumption in the process.

One of IGZO’s other benefits is that it is highly scalable, allowing for much higher resolution displays with greatly increased pixel densities. Sharp has already announced plans for panels with 600 pixels per inch. This can be accomplished more easily than with a-Si TFT types due to the smaller transistor size.

Smaller IGZO transistors are also touting superior noise isolation compared to a-Si, which should result in a smoother and more sensitive user experience when used with touchscreens. When it comes to IGZO OLED, the technology is well on the way, as Sharp has just unveiled its new 13.3-inch 8K OLED display at SID-2014.

Essentially, IGZO strives to reach the performance benefits of LTPS, whilst keeping fabrications costs as low as possible. LG and Sharp are both working on improving their manufacturing yields this year, with LG aiming for 70% with its new Gen 8 M2 fab. Combined with energy efficient display technologies like OLED, IGZO should be able to offer an excellent balance of cost, energy efficiency, and display quality for mobile devices.

Innovations in display backplanes aren’t stopping with IGZO, as companies are already investing in the next wave, aiming to further improve energy efficiency and display performance. Two examples worth keeping an eye are on are Amorphyx’ amorphous metal nonlinear resistor (AMNR) and CBRITE.

This developing technology can be manufacturing on a process that leverages a-Si TFT production equipment, which should keep costs down when it comes to switching production, whilst also offering a 40 percent lower cost of production compared with a-Si. AMNR is also touting better optical performance than a-Si and a complete lack of sensitivity to light, unlike IGZO. AMNR could end up offering a new cost effective option for mobile displays, while making improvements in power consumption too.

CBRITE, on the other hand, is working on its own metal oxide TFT, which has a material and process that delivers greater carrier mobility than IGZO. Electron mobility can happily reach 30cm²/V·sec, around the speed of IGZO, and has been demonstrated reaching 80cm²/V·sec, which is almost as high as LTPS. CBRITE also appears to lend itself nicely to the higher resolution and lower power consumption requirements of future mobile display technologies.

Smartphones are already benefiting from improvements in screen technology, and some would argue that things are already as good as they need to be, but the display industry still has plenty to show us over the next few years.

TFT active-matrix is a key technology for display manufacturing such as AMLCD and AMOLED display. Past, current and future TFT technologies are reviewed and discussed with the use of amorphous silicon (a-Si), low-temperature poly-Si (LTPS), organic and oxide semiconductors. TFT technologies based on a-Si:H and LTPS are mature enough, but the TFTs with oxide and organic semiconductors are still many issues to be solved for large scale manufacturing. Currently, display manufacturing based on a-IGZO TFT backplane is hot issue because a-Si:H production line can be easily modified to that for IGZO TFTs.

U.S would have smartphones, accounting for around 81% of the region"s population. Multiple industrial manufacturers are seeking to release cutting-edge smartphones with cutting-edge features like 5G connectivity and IGZO screens in response to the spike in adoption of smartphones and the appearance of impending 5G technology. This is anticipated to help the IGZO display market in U.S flourish.

China consumer electronics company announce the launch of its initial 85-inch 8K 120Hz screen world showcase industry conferencing. The TV offers a contrast of much more over 5000:1 on its 1G1D elevated Display screen, which would be IGZO technology, and consumes 30% less electricity than TVs of a similar size. It is projected that many new product introductions would boost IGZO display sales in the following years.

The display technology industry has seen a significant expansion in the production of LCD panels with IGZO (indium gallium zinc oxide) thin-film transistor (TFT) backplane.WitsView, a division ofTrendForce, estimates that the global production capacity of IGZO panels by area will reach about 6.9 million square meters this year, up 45% from 2015. A Gen-8.5 fab owned by major Chinese panel supplier CEC-Panda is currently responsible for much of this capacity expansion.

Apple is the first electronics device maker to adopt IGZO, using this type of panel for iPads in 2011 and 2012. While Apple has helped generated a wave of interests for this technology in the display market, the growth of IGZO products have been constrained by a host of issues. Getting related patents have been difficult, and there are still technological and yield-rate barriers to overcome. The spiraling price competition in different application markets are also compressing the overall market share of IGZO panels.

“Not only are IGZO products unable to establish a larger presence in the mid- and large-size panel markets, they are also having difficulty competing with the more mature LTPS technology in the small-size segment,” said Boyce Fan, senior research manager at WitsView. “Right now, Apple is the only major source of demand.”

Foxconn’s acquisition of Sharp has again put IGZO under the spotlight. Foxconn is currently considering increasing its investments in the technology and expanding its scale of adoption. Fan pointed out that the future success of IGZO panels in the display market will still hinge on Apple. There will be a rising, constant demand in the IGZO market if the U.S. electronics giant uses the technology for other product lines in addition to iPads. Suppliers in turn will be able to allocate their capacities for IGZO panels with some certainty and expand their production later on.

AMOLED has been getting increasing attention from panel suppliers competing in the smartphone display market. LTPS is now the dominant backplane technology for smartphone AMOLED panels. However, IGZO has lower current leakage rate than LTPS and thus consumes less power. With this advantage, IGZO has an opportunity to challenge LTPS in the potential AMOLED smartphone panel market.

Sharp has long been the main supplier of IGZO panels to Apple and already reached a high level of maturity in terms of manufacturing. WitsView estimates that Sharp will account for 33% of the global IGZO panel capacity area this year. LG Display (LGD) and Samsung Display (SDC) are also increasing their IGZO panel production in response to the iPad demand and possibility of Apple using the technology in other product lines. Together, the South Korean panel makers will constitute 28% of the global IGZO capacity this year. In sum, Sharp, LGD and SDC are expected to become the dominant IGZO panel suppliers in Apple’s supply chain.

Taiwan-based panel makers are more conservative in their investments of IGZO panel manufacturing as they lack orders from Apple. China’s CEC-Panda, on the other hand, has made huge investments in the technology because it has received the know-how and support from Sharp. The Chinese supplier’s Gen 8.5 fab in particular has added a considerable amount of capacity for IGZO panels of all sizes. According to WitsView, CEC-Panda’s share of the global IGZO panel capacity will come to 39%, making the company the largest IGZO panel supplier outside of Apple’s supply chain.

New drivers are opening up new frontiers in the display industry, resulting in technological innovation and the expansion and diversification of the market. This article summaries some of these recent developments and research from IDTechEx"s brand new report "Metal Oxide TFT Backplanes for Displays 2013-2018: Analysis, Trends, Markets" (http://www.IDTechEx.com/oxide).

The display industry has been experiencing rapid change. The centre of gravity has shifted away from Japan to Korea. This trend was made abundantly clear recently when Panasonic and Sharp announced that they are expecting a staggering combined loss of $15.2 billion in 2012. In fact, Sharp has already expressed "material doubt" about its survival.

This trend has been in the making during the past decade and the Japanese display giants are set to lose all the profits they accumulated during the past twenty years. There are many reasons for this decline, but chief amongst them has been the inability to bet on the right future technologies for the right markets. The market and technological landscape in the display has been experiencing rapid change, and Korean companies have largely made the right bets and investment decisions.

This changing market and technological scene not only creates opportunities and risks for display manufactures, but for all those involved in existing and emerging value chains. Many material suppliers, equipment makers and technology providers will stand to benefit, while others will see their market share and revenues dwindle.

Metal oxide thin film transistors (TFTs) are a key emerging technology in this space. They offer a set of compelling characteristics that make them a good fit in the emerging scene of the display industry. Their set of properties makes a good match for sustaining several underlying market megatrends that are shaping the industry. Indeed, Sharp has already launched 7-inch LCD display tablet based on IGZO backplanes. The intended benefits are high resolution, low power consumptions and of course product differentiation.

Metal oxide TFTs are however stepping into crowded technological space in which many backplane solutions already exist, including various forms of silicon and organic TFTs. Many are mature, proven and cost-effective solutions, while others offer a different package of characteristics than metal oxides. None however are one-size-fits-all solutions for all market needs and segments.

At the same time however, there are still numerous unresolved technical challenges, including the question of persistent photoconductivity and narrow processing window. Metal oxides are a broad family of materials and the final choice of the best material system and the best corresponding device architecture are not yet settled. The specifics of the manufacturing process and recipes too are in a state of flux. But it is nonetheless clear that they will play a role in future displays.

Several major trends have been driving technological innovation in the display industry since its early days. These trends include image quality, screen size, portability and form factor. While these trends still remain strong undercurrents, new drivers are being introduced that will play a more prominent role in shaping the future of the industry.

These new drivers will open up new frontiers, both on the technology and the market side. Indeed, they enable displays to both expand their existing markets and to diversify into new spaces. They will also fragment the market, at least initially. These major drivers that are set to change the display landscape include product differentiation, flexibility, 3D, transparency, system-on-panel, power savings, interconnectivity and screen size, and new front plane technologies.

Critically, these new trends can only be sustained so long as the underlying technology can deliver the required performance demands. This is critical because the new functional needs will stretch many existing solutions beyond their performance limits, suggesting that alternative solutions will be required. One vital piece of technology that largely sets the limits of display industry is the backplane technology. The backplane is responsible for turning the individual pixels ON and OFF. It is composed of thin film transistors, which act as the switches.

The over-arching trends in the industry are also changing the backplane requirements on several fronts. Product differentiation is resulting in multiplicity of lighting/display technologies, with each demanding a different power output and refresh rate from the backplane. For example, OLED is being increasingly adopted as a means of differentiating products. This in turn is changing the power out and spatial uniformity requirements that the backplane technology must satisfy.

Flexible displays are being developed to offer robustness in the short term, while in the long term they will aim at resolving the conflict between two diverging mega trends by making large-sized and portable devices possible. This push towards flexibility is opening up room for a new value chain consisting of new material systems. This is because many existing solutions are failing the flexibility tests, including many existing backplane solutions.

3D and ultra-high resolution displays mandate higher refresh rates, stretching the switching speed requirements past the capability limits of today"s dominant technologies, such as amorphous silicon (aSi) TFTs. System-on-panel thinking is requiring ever more processing power to be integrated onto the panel, and therefore the backplane.

This new report by IDTechEx (Metal Oxide TFT Backplanes for Displays 2013-2018: Analysis, Trends, Markets www.IDTechEx.com/oxide) analyzes major drivers that are shaping the display industry. The major trends examined in detail include product differentiation, size and scaling, power savings, prolonged lifetime, 3D, mechanical flexibility, rimless designs, etc. It analyses how these market drivers create market fragmentation and market opportunities.

Figure 2. Radar chart showing the technological suitability of different backplane technologies for sustaining megatrends in the OLED display industry

An IGZO display is a not a type of a display panel. To be more specific, an IGZO display is any display panel that uses a backplane thin-film transistor or TFT made of indium gallium zinc oxide or IGZO semiconductor material. Hence, IGZO display technology is compatible with different types of display panels such as twisted nematic or TN LCD, in-plane switching or IPS LCD, and organic light emitting diode or OLED display. To understand further what an IGZO display is, it is important to understand its properties or characteristics and thereby, it benefits or advantages, as well as its limitations and disadvantages.

Note that more light passes through an IGZO-based TFT than silicon-based TFTs such as amorphous silicon or aSi-TF because it is naturally transparent and more compact. Nonetheless, the primary advantage of an IGZO display is its natural transparency.

This transparency translates to energy efficiency. To be more specific, compared to an LCD equipped with an aSi-TFT, an LCD based on an IGZO TFT uses less power due to the reduced need for backlighting intensity. In the case of an OLED, an IGZO TFT reduces the brightness output of individual organic diode. Display panels based on arguably consumes less power than an aSi display while still producing brighter images.

An IGZO semiconductor has 30 to 50 times more electron mobility than amorphous silicon, thus allowing a smaller physical footprint without compromising conductivity. This higher electron mobility corresponds to more specific benefits.

For instance, note that the size of transistors affects the size of the pixel. Due to a higher electron mobility, another advantages of IGZO display when compared to an aSi display is higher pixel density within a smaller display real estate.  Earlier IGZO display prototypes had crammed 498 pixels per inch within a six-inch footprint.

It is also worth mentioning that backlighting is obstructed in high pixel density LCD based on aSi-TFT. To compensate, these aSi-based displays consume more power for a more intense backlighting. Power consumption requirement increases with an increase in thepixel density of an aSi-TFT LCD. This is not a problem in IGZO-based TFT LCDs.

IGZO has electron mobility that is nearly as high as low-temperature polysilicon or LTPS. However, LTPS has a higher current leakage that results in high power consumption. On the other hand, although aSi has lower current leakage, remember that it also has lower electron mobility than both IGZO and LTPS

The low current leakage and high electron mobility of IGZO give it a more advantageous current flow than aSi and LTPS. This advantage means that the transistors in an IGZO display do not have to be refreshed continuously while displaying a still image because it can retain the active state of its pixels longer due to its advantageous current flow.

On the other hand, displays based on aSi or LTPS need to overwrite still image data through a continuous refresh. Hence, when compared to an IGZO display, an aSi-TFT or LTPS-TFT display consumes 80 to 90 percent more power, particularly when displaying still images such as photographs or documents.

Another benefit of IGZO TFT and thus, another advantage of IGZO display is less noise influence. This characteristic is based on the fact that an IGZO is an intermittent type of semiconductor.

To understand further, note that the drive in an IGZO display does not need to be continuous. This allows touch input to be more sensitive or responsive. Although noise is a consequence of touch-sensitive displays, the noise generated by touching an IGZO display is very brief, thereby resulting in a more accurate detection of even the faintest signal.

An IGZO display with a higher degree of touch sensitivity can pick up thinner and finer lines than non-IGZO displays, notably silicon-based TFT displays. Writing on an IGZO display has a closer feel as writing on a paper, thus mimicking natural handwriting input.

Note that IGZO is a metal oxide. The high reactivity of oxygen increases susceptibility to very low voltage sensitivity, thus resulting in operation disruption and possible internal failures.

Another disadvantage is lower uniformity of electron mobility when compared to aSi and LTPS that may result in differences in product quality across similar products or batch of units. The same low uniformity of electron mobility may result in operation disruptions or inconsistencies of an individual IGZO-based product.

IGZO is made from rare-earth metals indium and gallium. The rarity of these metal introduces risks in costs and procurement that could affect mass production and subsequently, expansive applications and standardization in consumer electronic devices due to supply shortages.

Other manufacturing issues collectively represent another disadvantage of IGZO display. To be specific, the current obstacle to mass-producing IGZO is synthesis. The most common used synthesis method in the industry, the Pulsed Laser Deposition or PLD, requires expensive equipment and a considerable amount of time for each output to adapt to environmental conditions. A possible alternative to PLD is combustion synthesis, but its feasibility and practicality needs more research.

Remember that one of the advantages of IGZO display is a better response time than aSi-TFT and other silicone-based TFT displays. However, transmissive display technologies such as  TN LCD and IPS LCD inherently have slow response times when compared to emissive display technologies, thus rendering this advantage almost negligible. An OLED display based on IGZO TFT can still take advantage of this faster response time.

The advantages of IGZO display revolve around its physical properties that enable it to operate under lesser power requirements than its silicone-based counterparts while featuring higher density display regardless of size. These advantages benefit consumer electronic devices such as smartphones and portable computers.

It is also important to reiterate the fact that IGZO is not a type of display panel but rather a type of display technology or manufacturing configuration. This configuration applies to different types of display panels such as TN LCD and TN IPS, as well as OLED or AMOLED displays.

There is also no considerable difference between an LCD or OLED based on aSi-TFT and an LCD or OLED based on IGZO, specifically when it comes to image quality and color reproduction accuracy. However, as discussed above, IGZO-based display panels have considerable advantages such as substantial power saving and smaller physical footprint without compromising pixel density and brightness.

A hybrid between IGZO and LTPS is possible. Apple Inc. demonstrated in its Apple Watch devices that it is possible to combine silicon-based and oxide-based materials with the so-called low-temperature polycrystalline oxide or LTPO display.