Thin-film Circuits Research Articles

MILC PMOS Poly-Silicon TFT Circuits and Application in SOP

Research towards thin film circuits is one of the most attractive directions of the large-area electronics and flexible electronics. In this work, the research on TFT shift register circuit which is critical for system integration on panel (SOP) is presented. The whole circuit is composed of MILC PMOS poly-Si TFTs. The TFT device exhibited field-effect mobility of 65.21cm2/Vs, threshold voltage of -3.5V and sub-threshold swing of 0.56V/dec. Some special design considerations were adopted to improve the robustness of the circuits. The whole shift register is composed of as many as 180 stages and exhibited well performance with frame frequency from 22Hz to 220Hz at the power supply voltage of 11V. No signal attenuation and distortion appeared from the first to the final stage. The effect of bootstrapping and dynamic behavior is analyzed. The fabrication and reliability analysis are also discussed in this paper. Overall, the high performance driver circuits based on our MILC PMOS process are possible and have the potential in the application of SOP.

Room-temperature solution-processed high-k gate dielectrics for large area electronics applications

One of the key challenges to manufacture low cost circuits (e.g. RFID tags) and backplanes on flexible substrates lies in the realization of a reliable gate-dielectric with a high specific capacitance required for low voltage, high current drive. Flexible substrates necessitate deposition techniques with process temperatures lower than 150 °C, making the production of high quality gate dielectric materials more difficult. Here we show a promising integration scheme for thin film circuits using anodization. Aluminium oxide can be fabricated at low cost by anodization of aluminium at room temperature, giving rise to an ultra-thin, smooth, and dense gate dielectric. Starting from a blank Al film deposited on an arbitrary substrate, we anodize part of the metal to Al 2 O 3 and pattern the Al / Al 2 O 3 stack into appropriate islands in a single patterning step. Overetch of the Al gate allows the further processing of source-drain contacts without side leakage between source and gate at the edge of the gate islands. The process also allows for defined connections between source metal and gate metal as needed in circuits. With this process, we show pentacene and Ga–In–Zn–O TFTs and pentacene circuits (inverters and 19 stage ring oscillators) with channel-length down to 3 μm, operating at voltages as low as 2 V. They allow us to assess the possibility to use anodized Al 2 O 3 as gate dielectric for TFTs in circuits.

Carbon Nanotubes, Semiconductor Nanowires and Graphene for Thin Film Transistor and Circuit Applications

In this paper, we briefly review the use of carbon nanotubes and semiconductor nanowires, which represent a new class of nanomaterials actively studied for thin film transistors and electronics applications. Although these nanomaterials are usually synthesised at moderate to high temperatures, they can be transferred to any kind of substrate after growth, paving the way for the fabrication of flexible displays and large area electronics systems on plastic. Over the past few years, the field has progressed well beyond the realisation of elementary devices, since active matrix displays driven by nanowire thin film transistors have been demonstrated, as well as the fabrication of medium scale integrated circuits based on random arrays of carbon nanotubes. Also, graphene, a new nanomaterial has appeared in the landscape; although it is a zero gap semiconductor, it can still be used to make transistors, provided narrow ribbons or bilayers are used. Graphene is also a serious contender for the replacement of oxide-based transparent conducting films.

Carbon Nanotubes, Semiconductor Nanowires and Graphene for Thin Film Transistor and Circuit Applications

Carbon Nanotubes, Semiconductor Nanowires and Graphene for Thin Film Transistor and Circuit Applications

Organic Electronics on Banknotes: Organic Electronics on Banknotes (Adv. Mater. 5/2011)

Organic thin-film transistors and organic integrated circuits can be fabricated directly onto the surface of banknotes, report Ute Zschieschang and co-workers on p. 654. The transistors have a field-effect mobility of about 0.2 cm2 V−1 s−1 and operate with voltages of 3 V. For an array of 100 transistors fabricated on a 5 Euro note, a yield of 92% working devices has been obtained, pre-senting organic electronics as a possible route to improved anti-counterfeiting strategies.

Multi-access drug delivery network and stability

A novel design of a multi-drug delivery network and diagnosis using a molecular network is proposed. By using a pair of tweezers to generate the intense optical vortices within the PANDA ring resonator, the required molecules (drug volumes) can be trapped and moved dynamically within the molecular bus networks, in which the required drug delivery targets can be achieved within the network. The advantage of the proposed system is that the diagnostic method can be used within a tiny system (thin film device or circuit), which is available as an embedded device for diagnostic use in patients. In practice, the large molecular networks such as ring, star, and bus networks can be integrated to form a large drug delivery system. The channel spacing of the trapped volumes (molecules) within the bus molecular networks can be provided by using the appropriate free spectrum range, which is analyzed and discussed in the terms of crosstalk effects. In this work, crosstalk effects of about 0.1% are noted, which can be neglected and does not affect the network stability.

Organic dual DC-DC upconverter on foil for improved circuit reliability

A report is presented on the design and measurement of one of the first dual DC-DC upconverters implemented in an organic thin-film technology on foil providing output voltages beyond the upper and lower power supply voltages. The converter generates bias voltages around +50 and −40 V from a 20 V power supply. The upconverted voltage range is sufficient to bias backgates of transistors in dual-gate thin-film transistor technologies, which improves the reliability of analogue as well as digital thin-film circuits.

Low-Resistivity and Adhesive Sputter-Deposited Cu–Ca Films with an Intermediate Oxide Layer

We investigated a method of producing low-resistivity and adhesive sputter-deposited copper alloy films with an intermediate oxide layer that retains its adhesion after hydrogen annealing for applications of electric interconnections for thin film circuits and liquid crystal displays. The formation of an intermediate copper oxide layer between a copper film and a substrate by sputter deposition in the presence of oxygen enhances adhesion. However, when such films are exposed to hydrogen at elevated temperatures, hydrogen penetrates the films and reduces copper oxide. This reaction generates water molecules, which aggregate at the interface between the copper film and the substrate. As a result, microvoids form at the interface, degrading the film adhesion. Sputter-deposited films with an intermediate oxide layer produced from a Cu–Ca target are adhesive even after hydrogen annealing. As films deposited in pure argon have low resistivities, it is possible to form low-resistivity and adhesive metallization.

61.1: Invited Paper: ZnO Thin Film Transistors and Circuits on Flexible Polymeric Substrates by Low‐Temperature PEALD

AbstractWe report using a novel, weak oxidant, plasma‐enhanced atomic layer deposition (PEALD) process at 200 °C to fabricate stable, high mobility ZnO thin film transistors (TFTs) and fast circuits on glass and polyimide substrates. Weak oxidant PEALD provides a simple, fast deposition process that results in uniform, conformai semiconductor and dielectric layers and enhancement‐mode MOSFETs from uncompensated films. Highly conformai PEALD Al2O3 layers provide a high yield dielectric on rough plastic substrates for both PEALD ZnO TFTs and cross‐overs. Our PEALD ZnO TFTs have field‐effect mobility of >20 cm2/V·s on polyimide substrates with excellent bias stress stability. TFTs biased continuously for 40,000s showed <50 mV threshold voltage shift. We also report fast PEALD ZnO circuits on polyimide substrates with propagation delay <20 ns/stage for VDD = 18 V.

Fast Flexible Plastic Substrate ZnO Circuits

We report thin-film transistors (TFTs) and circuits fabricated on flexible plastic substrates using ZnO thin films deposited by plasma-enhanced atomic layer deposition at 200°C. Crossover test structures fabricated on flexible substrates have a good yield, and ZnO TFTs have a field-effect mobility of 20 cm2/V · s. The 15-stage ring oscillators are operated at > 2 MHz with a supply voltage of VDD = 18 V, corresponding to a propagation delay of < 20 ns/stage. To the best of our knowledge, these are the fastest oxide-semiconductor circuits on flexible substrates reported to date.

Fast, simple ZnO/organic CMOS integrated circuits

Hybrid organic–inorganic CMOS thin-film circuits are a simple, potentially low-cost, approach for large-area, low-power microelectronic applications. We have used atmospheric pressure processes to deposit inorganic ZnO and organic diF TES-ADT semiconductor layers and an Al 2O 3 gate dielectric. The organic semiconductor uses a contact-treatment-related microstructure that allows circuits to operate without directly patterning the organic layer. Using a simple 4-mask process with bifunctional Ti/Au contacts for both ZnO and organic transistors, 7-stage ring oscillators were fabricated and operated at >500 kHz corresponding to a propagation delay of <150 ns/stage at a supply bias of 35 V. These are the fastest organic–inorganic CMOS circuits reported to date.

Cascaded single-stage distributed amplifier using DPHEMT devices for multioctave performance

This paper describes a multioctave (2---18 GHz) distributed amplifier design using the concept of cascaded reactively terminated single-stage distributed amplifier (CRTSSDA) configuration for EW applications. The concept of CRTSSDA is demonstrated to provide broadband performance with high gain, reduced power consumption, circuit stability and superior power-added efficiency compared to conventional distributed amplifiers using the same number of active devices. The broadband amplifier employing three-CRTSSDA is designed and fabricated using three different DPHEMT devices in the three respective stages of the design to further enhance the amplifier's efficiency performance. The amplifier achieved an associated gain level above 26 dB with flatness of <± 0.5 dB, an average power-added efficiency in access of 27% at an output power of 25 dBm across 2---18 GHz with an efficiency peak of 30% at 12 GHz. The input and output VSWR of better than 2:1 was achieved. Furthermore, the CRTSSDA provides a cost-effective solution when compared to the conventional travelling wave amplifier as only half the number of active devices is used. Fabrication of the amplifier was carried out by using the conventional thin-film microwave integrated circuit technology. The CRTSSDA is also disposed to realization by monolithic circuit technology.

Key near-term R&D issues for continuous improvement in CIS-based thin-film PV modules

In a large-area approach up to 60 cm×120 cm size, monolithically integrated CIS-based thin-film PV modules have come to the efficiency level of 13%. The key near-term R&D issues to realize continuous improvement in CIS-based thin-film PV modules are related to their competitiveness against the crystalline-Si PV modules. In this contribution, the following three issues are discussed. The first and main issue is how important it is to understand the interfaces in the CIS-based thin-film circuit to improve the efficiency, because CIS-based thin-film circuits are fabricated in a stacked structure of four or five thin films. The second and third issues are how beneficial it is to develop the packaging and material recycle technologies in order to reduce the production cost.

Dynamic Characteristics of Metal-Induced Laterally Crystallized Polycrystalline Silicon Thin-Film Transistor Devices and Circuits Fabricated with Asymmetric Precrystallization

The effects of a crystal growth joint in metal-induced laterally crystallized polycrystalline silicon thin-film transistor devices and circuits employing the precrystallization method were studied. It was found that the joint after symmetric precrystallization results in slight degradation in field-effect mobility and little degradation in leakage current, but its location after asymmetric precrystallization has a close connection with degradation only in leakage current and not in mobility. Moreover, DC bias-induced changes in the performance of ring oscillators were studied. Inverters fabricated using a fully asymmetric precrystallized silicon film had very high dynamic and stable performances, compared with inverters fabricated using a symmetric precrystallized silicon film.

Fabrication conditions for solution-processed high-mobility ZnO thin-film transistors

Stable, solution-processed, non-toxic, high-mobility thin-film semiconductors are required for fabricating low-cost thin-film transistor (TFT) arrays and circuits to enable ubiquitous large-area and ultra low-cost electronics. Most thin-film semiconductors reported to date have been unable to meet the mobility, stability, safety, and cost requirements for this emerging technology, thus precluding their adoption in practical applications. Here, we report the preparation of stable, non-toxic, transparent, high performance zinc oxide (ZnO) thin-film semiconductors via thermal processing of solution-deposited precursor thin films in air. The process conditions influence the performance of the TFTs. By optimizing the fabrication conditions, the prepared ZnO thin-film semiconductor has a well-controlled, preferential crystal orientation and densely packed ZnO crystals, exhibiting excellent field-effect performance characteristics with mobility far exceeding those of hydrogenated amorphous silicon (a-Si:H). Consistently reproducible mobility ∼5–6 cm2V−1s−1 and current on-to-off ratio ∼105–106 have been obtained, while the production cost was controlled as low as possible. This potentially opens up application opportunities inaccessible by a-Si:H technology and renders otherwise costly large-area electronics affordable.

A comparative study of plasma-enhanced chemical vapor gate dielectrics for solution-processed polymer thin-film transistor circuit integration

This paper considers plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) and silicon oxide (SiOx) as gate dielectrics for organic thin-film transistors (OTFTs), with solution-processed poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] (PQT-12) as the active semiconductor layer. We examine transistors with SiNx films of varying composition deposited at 300 °C as well as 150 °C for plastic compatibility. The transistors show over 100% (two times) improvement in field-effect mobility as the silicon content in SiNx increases, with mobility (μFE) up to 0.14 cm2/V s and on/off current ratio (ION/IOFF) of 108. With PECVD SiOx gate dielectric, preliminary devices exhibit a μFE of 0.4 cm2/V s and ION/IOFF of 108. PQT-12 OTFTs with PECVD SiNx and SiOx gate dielectrics on flexible plastic substrates are also presented. These results demonstrate the viability of using PECVD SiNx and SiOx as gate dielectrics for OTFT circuit integration, where the low temperature and large area deposition capabilities of PECVD films are highly amenable to integration of OTFT circuits targeted for flexible and lightweight applications.

선결정화법을 이용한 금속 유도 일측면 결정화에 의해 제작된 다결정 실리콘 박막 트랜지스터 소자 및 회로의 전기적 특성 개선 효과

The phase transformation in a film influences its surrounding. Effects of the precrystallization method, which removes influences on gate oxide caused by lateral crystallization, in metal-induced unilaterally crystallized polycrystalline silicon thin-film transistor devices and circuits were studied. Device by the method was shown to have a higher current drive, compared with conventional postcrystallized device. Moreover, we studied DC bias-induced changes in the performance of ring oscillator. PMOS inverters fabricated using precrystallized silicon films have very high dynamic and stable performance, compared with inverters fabricated using postcrystallized silicon films.

Dynamic Characteristics of Multi-Channel Metal-Induced Unilaterally Precrystallized Polycrystalline Silicon Thin-FilmTransistor Devices and Circuits

Electrical properties of multi-channel metal-induced unilaterally precrystallized polycrystalline silicon thin-film transistor (MIUP poly-Si TFT) devices and circuits were investigated. Although their structure was integrated into small area, reducing annealing process time for fuller crystallization than that of conventional crystal filtered MIUP poly-Si TFTs, the multi-channel MIUP poly-Si TFTs showed the effect of crystal filtering. The multi-channel MIUP poly-Si TFTs showed a higher carrier mobility of more than 1.5 times that of the conventional MIUP poly-Si TFTs. Moreover, PMOS inverters consisting of the multi-channel MIUP poly-Si TFTs showed high dynamic performance compared with inverters consisting of the conventional MIUP poly-Si TFTs.

Medium-scale carbon nanotube thin-film integrated circuits on flexible plastic substrates

The ability to form integrated circuits on flexible sheets of plastic enables attributes (for example conformal and flexible formats and lightweight and shock resistant construction) in electronic devices that are difficult or impossible to achieve with technologies that use semiconductor wafers or glass plates as substrates. Organic small-molecule and polymer-based materials represent the most widely explored types of semiconductors for such flexible circuitry. Although these materials and those that use films or nanostructures of inorganics have promise for certain applications, existing demonstrations of them in circuits on plastic indicate modest performance characteristics that might restrict the application possibilities. Here we report implementations of a comparatively high-performance carbon-based semiconductor consisting of sub-monolayer, random networks of single-walled carbon nanotubes to yield small- to medium-scale integrated digital circuits, composed of up to nearly 100 transistors on plastic substrates. Transistors in these integrated circuits have excellent properties: mobilities as high as 80 cm(2) V(-1) s(-1), subthreshold slopes as low as 140 m V dec(-1), operating voltages less than 5 V together with deterministic control over the threshold voltages, on/off ratios as high as 10(5), switching speeds in the kilohertz range even for coarse (approximately 100-microm) device geometries, and good mechanical flexibility-all with levels of uniformity and reproducibility that enable high-yield fabrication of integrated circuits. Theoretical calculations, in contexts ranging from heterogeneous percolative transport through the networks to compact models for the transistors to circuit level simulations, provide quantitative and predictive understanding of these systems. Taken together, these results suggest that sub-monolayer films of single-walled carbon nanotubes are attractive materials for flexible integrated circuits, with many potential areas of application in consumer and other areas of electronics.

Single-grain Si thin-film transistors SPICE model, analog and RF circuit applications

Single-grain thin-film transistors (SG-TFTs) fabricated inside location-controlled using μ-Czochralski process exhibit SOI-FETs like performance despite processing temperatures remaining below 350°C. Thus, the SG-TFT is a potential technology for large-area highly-integrated electronic system and system-in-package, taking advantage of the system-on-flexible substrate and low manufacturing cost capabalities. The SG-TFT is modeled based on the BSIMSOI SPICE model where the mobility parameter is modified to fit the SG-TFT behavior. Therefore, analog and RF circuits can be designed and benchmarked. A two-stage telescopic cascode operational amplifier fabricated in a prototype 1.5μm SG-TFT technology demonstrates DC gain of 55dB and unity-gain bandwidth of 6.3MHz. A prototype CMOS voltage reference demonstrates a power supply rejection ratio (PSRR) of 50dB. With unity-gain frequency, fT, in the GHz range, the SG-TFT can also enable RF circuits for wireless applications. A 12dB gain RF cascode amplifier with integrated on-chip inductors operating in the 433MHz ISM band is demonstrated.