Marc Ameys

Organic CMOS Line Drivers on Foil

In this paper, the design of a low-voltage line driver in a complementary organic technology on foil is presented. The behavior and the variability of circuits are predicted by means of transistor modeling and statistical characterization. The comparison of measurements and simulations of simple digital blocks verifies the effectiveness of the design approach. A transmission-gate based 32-stage line driver and a fully-static one are shown. It is also shown that, based on the statistical organic thin-film transistor (OTFT) characterization, the fully-static logic style is a more suitable choice for implementing line drivers in this technology. The implemented fully-static line driver, which is comprised of 1216 transistors, has the highest transistor count reported for a complementary organic circuit to date. It works at supply voltages from 10 V to as low as 3.3 V, reaching a 1 kHz clock frequency, and occupying an area of 25 ×4.7 mm2. The drivers are implemented in a technology compatible with that of flat-panel display backplanes and are tested with a QQVGA AMOLED display.

Integrated Line Driver for Digital Pulse-Width Modulation Driven AMOLED Displays on Flex

An integrated scan-line driver, driving half a QQVGA flexible AMOLED display using amorphous-IGZO backplane technology on foil, has been designed and measured. A pulse-width modulation technique has been implemented, enabling to drive the OLEDs with a duty cycle up to almost 100%. The digital driving method also results in a 40% static power reduction of the display. Dynamic logic and bootstrapping techniques enabled the use of clock frequencies up to 300 kHz in unipolar amorphous-IGZO technologies on foil.

Integrated UHF a-IGZO energy harvester for passive RFID tags

We present an energy harvester composed of a dipole antenna, matching network and a rectifier based on thin-film metal-oxide (amorphous Indium-Gallium-Zinc Oxide, IGZO) semiconductor Schottky diodes, operating at 868MHz. S-parameters measurements show that the integrated single IGZO Schottky diodes have a cutoff frequency over 1.8GHz at 0V bias. Large signal analysis of the integrated double-half wave rectifier shows a cut-off frequency of 1.1GHz. Our harvester generates 1.3V at 15 cm from an emitter emitting 15dBm at 868MHz.

30.2 Digital PWM-driven AMOLED display on flex reducing static power consumption

The efficiency of small-molecule OLED devices increased substantially in recent years, creating opportunities for power-efficient displays, as only light is generated proportional to the subpixel intensity. However, current active matrix OLED (AMOLED) displays on foil do not validate this power-efficient advantage, as too much power is lost in the AM backplane. AMOLED displays use the analog voltage on the gate of a drive transistor (e.g. M1 in Fig. 30.2.1) to control the pixel current and hence the pixel brightness. Accurate and uniform pixel currents can only be obtained when transistor M1 is driven is saturation. In highresolution technologies on foil, transistor parameters W, L and the mobility μ are limited by technology, imposing a minimal VGS-VT to obtain sufficient current, i.e. VGS-VT > 4V for a-IGZO on foil [1]. Subsequently, to obtain saturation, VDS > 4V, which translates in a static backplane power loss surpassing the OLED power consumption (see red stars in Fig 30.2.1). However, when the OLED pixel impedance around a specific reference current can be matched along a display column line, the accurate pixel current control can be imposed by current DACs implemented in external silicon display column drivers. In this work, we operate M1 as a switch and pixel intensity variations are obtained using Pulse Width Modulation (PWM) of a predefined pixel current, i.e. 2μA/pixel [80*80μm2] (which corresponds in our OLED technology to a light output of 2000Cd/m2). When, in a future implementation the external DACs are calibrated at 0.2μA/pixel, the full brightness would correspond to the typical display brightness of a portable PC, i.e. 200Cd/m2. This concept enables us to reduce the display power voltage at full brightness from 8.2V in a classical AMOLED display on foil configuration to 5V (measured) and for future implementations even down to 4V (see Fig. 30.2.1). As the OLED current load remains equal, a corresponding static power reduction of the display (and increased battery lifetime) is obtained. Digital driving methods of AMOLED displays have been shown before. However, ΔΣ techniques [2] still integrate charge packets on the gate of M1 and hence do not solve the power issue on foil. Other PWM techniques [3] activate only a single active line in the linedriver yielding difficulties to obtain color depths above 6 bits. When multiple independent linedrivers are implemented and their output is multiplexed to alternately drive a single select line, a higher color depth can be obtained [4]. This leads however to a bulky linedriver, which is hard to get within an e.g. 80μm pitch. The design and implementation of a compact integrated linedriver on foil enabling multiple alternating active signals through a single shift register is demonstrated here.

15.2 A flexible ISO14443-A compliant 7.5mW 128b metal-oxide NFC barcode tag with direct clock division circuit from 13.56MHz carrier

Flexible low-cost RFID/NFC tags have great potential to be embedded in everyday objects providing them a unique identifier or sensor readout facilitating the Internet-of-Everything, whereby a smartphone or tablet is the interface to the Internet-of-Things. The main challenge for flexible metal-oxide RFID tags is to fully comply with the ISO14443-A NFC standard to enable readout by standard NFC reader or handheld devices, due to the limited charge carrier mobility of the semiconductor and multiple sources of parameter variation caused by roughness, temperature and dimensional stability of the foils. Recent work by various groups [1–4] demonstrated only an incremental improvement in data rates from 50b/s to 396.5kb/s to be compatible with ISO14443 (105.9kb/s). In this work, we present a flexible metal-oxide NFC chip that is compliant with ISO14443-A, showcasing advancements on memory size, power consumption and a clock generation circuit.

An active artificial iris controlled by a 25-μW flexible thin-film driver

We show an active artificial iris based on solely thin-film components, wherein several LCD elements are controlled a metal-oxide TFT and by powered by thin-film photovoltaics (TFPV). Key aspects for the driver are size and low power consumption. We demonstrate power consumption down to 25μW for the full iris.

Organic Imager on Readout Backplane Based on TFTs With Cross-Linkable Dielectrics

We report on the fabrication of imagers based on organic semiconductors both in the photodiode layer and in the readout backplane. The photodiode is based on evaporated ultrathin (<;100 nm) stack of SubPc/C60, sensitive in the wavelength range between 300 and 650 nm. The readout circuit is a switch matrix fabricated with a solution processed semiconductor (XPRD30B01) and two solution processed, crosslinkable dielectrics (XDRD30B01). The readout TFTs (140/5-μm channel width/length, respectively) have leakage current lower than 1 pA with the ON-current higher than 0.1 μA. The 32 × 32 pixel imagers with pixel pitch down to 200 μm are demonstrated with mean dark signal of a few μA/cm2 and linear photoresponse up to the incident power of 100 μW. These results show feasibility of fabricating readout circuits with TFTs based on crosslinkable dielectrics. This enables reduction of two patterning steps (opening of the gate dielectric and of the encapsulation layer) to just photolithography, leading to simplification of the backplane manufacturing process.

Flexible selfbiased 66.7nJ/c.s. 6bit 26S/s successive-approximation C-2C ADC with offset cancellation using unipolar Metal-Oxide TFTs

Metal-Oxide thin-film transistors (TFTs) present unique opportunities to develop robust, low-cost and transparent electronics that can mechanically endure on flexible and stretchable substrates over large area in an industry compatible technology. Analog to digital converters (ADC) are an essential part of the Internet-of-Everything, where a multitude of sensing applications are envisaged, such as temperature and pressure sensor tags on human skin. In this work, dual-gate InGaZnO TFTs (IGZO) are demonstrated to achieve a 6-bit successive approximation (SAR) C-2C ADC operated at a clock of up to 400Hz and a power dissipation of 52.2µW at a power supply of Vdd=15V. The ADC achieves a differential nonlinearity (DNL) of 0.7LSB and an integral nonlinearity (INL) of 0.58 LSB using only n-type TFTs. A figure of merit (FoM) of 66.7nJ/c.s. is achieved from an ADC on flexible substrate.

Solving the technology barriers in flexible AMOLED displays

In this paper, we present some of the technology challenges and process temperature trade-offs when realizing AM OLED displays on thin flexible plastic films that can be mechanically bent to a roll radius of ~1 cm. We furthermore present complementary approaches to realize low-power, high resolution OLED displays using self-aligned IGZO TFT architecture; a novel driving method using a compact 2T-1C pixel engine.