Jae-Sup Lee

65.2: Distinguished Paper: World-Largest (6.5”) Flexible Full Color Top Emission AMOLED Display on Plastic Film and Its Bending Properties

The world largest flexible full color 6.5-inch active matrix organic light emitting diode (AMOLED) display with top emission mode on plastic film is demonstrated. The active matrix backplanes were fabricated using metal oxide thin film transistors (TFTs). The n-channel metal oxide TFTs on plastic film exhibited field-effect mobility of 17.8 cm2/Vs, threshold voltage of 0.4 V, on/off ratio of 1.1× 108, and subthreshold slope of 0.34 V/dec. These TFT performance characteristics made it possible to integrate scan driver circuit, demux switching and compensation circuit on the panel. Bending tests were performed with TFT backplane samples to determine critical curvature radius to which the panel can be bent without TFT performance degradation. The results were compared with the calculations that took into account thicknesses and mechanical constants of flexible substrate and of thin-film layers in AMOLED device.

Flexible full color organic light-emitting diode display on polyimide plastic substrate driven by amorphous indium gallium zinc oxide thin-film transistors

We have fabricated 6.5 in. flexible full-color top-emission active matrix organic light-emitting diode display on a polyimide (PI) substrate driven amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs). The a-IGZO TFTs exhibited field-effect mobility (μFE) of 15.1 cm2/V s, subthreshold slope of 0.25 V/dec, threshold voltage (VTH) of 0.9 V. The electrical characteristics of TFTs on PI substrate, including a bias-stress instability after 1 h long gate bias at 15 V, were indistinguishable from those on glass substrate and showed high degree of spatial uniformity. TFT samples on 10 μm thick PI substrate withstood bending down to R=3 mm under tension and compression without any performance degradation.

Experimental evidence of ballistic transport in cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field-effect transistors

We have investigated the electrical characteristics of cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field effect-transistors with 4nm radius and the gate length ranging from 22to408nm. We observed strong transconductance overshoot in the linear source-drain bias regime in the devices with channel length shorter than 46nm. The mean free path estimated from the slope of the zero-field one dimensional ballistic resistance measured as a function of device length was almost the same as this length.

Flexible AMOLED displays on stainless-steel foil

— The worlds thinnest flexible full-color 5.6-in. active-matrix organic-light-emitting-diode (AMOLED) display with a top-emission mode on stainless-steel foil was demonstrated. The stress in the stainless-steel foil during the thermal process was investigated to minimize substrate bending. The p-channel poly-Si TFTs on stainless-steel foil exhibited a field-effectmobility of 71.2 cm2/N-sec, threshold voltage of −2.7 V, off current of 6.7 × 1013 A/μm, and a subthreshold slope of 0.63 V/dec. These TFT performances made it possible to integrate a scan driver circuit on the panel. A top-emission EL structure was used as the display element, and thin-film encapsulation was performed to realize a thin and flexible display. The full-color flexible AMOLED display on stainless-steel foil is promising for mobile applications because of its thin, light, rugged, and flexible properties.

Challenges and directions of ultra low energy wireless sensor nodes for biosignal monitoring

This paper discusses design challenges and strategies for aggressively increasing energy efficiency of biosignal monitoring sensors. For the holistic understanding of energy efficiency, we introduce Energy Efficiency metric for all sensor communication blocks which include not only Rx/Tx RF&Analog, PLL and DSP/Modem but also Antenna and Power Management. Based on the metric, an ultra-low energy sensor node design at 2.36~2.5GHz is addressed from RFIC, DSP/Modem to Antenna. To tackle the stringent power requirements, we theoretically revisit the technology, circuits, architecture and system and explore the cross-layer power minimization algorithm.

Optimized Ultralow-Power Amplifier for OOK Transmitter With Shaped Voltage Drive

For a highly efficient ON-OFF keying (OOK) transmitter, a microwatt-level ultralow-power (ULP) driver and power amplifier (PA) are designed. For efficient amplification with very high optimum impedance in the ULP application, a class-C topology is implemented and loadpull simulations are carried out to show that the proposed PA can achieve good efficiency at high optimum load impedance without any harmonic tuning. In addition, a voltage-shaping driver is optimized together with the PA for an efficient drive. The proposed driver shapes the PA input voltage into a waveform having a small conduction angle. The shaped input voltage drives the PA to a saturated operation for good efficiency even if the supply voltage is low in the drive stage. The developed driver and PA are implemented in a CMOS 65-nm process and support a 1-Mb/s OOK modulated signal. The implemented PA achieves a drain efficiency of 50.8% at the -6.8-dBm output power and 49.8% at the -10-dBm output power when transmitting continuous 1 signal.

P-ARQ: Controllable PLL ARQ method for wireless low power communication

To minimize the power consumption of a wireless radio module, a cross layer optimization is essential. The energy consumption behavior heavily depends on the wireless medium access control (MAC) protocol, which controls the activity and the operating mode of wireless radio modules. The largest proportion of power in wireless radio module is consumed in the radio frequency (RF) analog. As the power consumption in the RF/Analog gets smaller, the power consumption of the phase-locked loop (PLL) in RF/Analog gets higher. In this paper, we propose a Controllable PLL (CPLL) and a controllable PLL automatic repeat request (P-ARQ) method. The CPLL is a new concept of PLL having activation and deactivation controllability. The proposed P-ARQ along with CPLL can conserve energy by reducing the number of PLL operations and extending the time to stay in the low power status of the CPLL. Simulation results show that the P-ARQ decreases the energy consumption by 18-32% in various transmission rates and channel environments.

An efficient rectifier for an RDA wireless power transmission system operating at 2.4 GHz

This paper describes the design and measurement of a full-bridge rectifier and a receiving antenna array operating at 2.4 GHz for wireless power transmission system applications, and with motivations to wirelessly charge an electronic device in the radiating near-field. A retrodirective antenna array (RDA) was also used in the system with high power gain to boost the overall received RF power at the input of the rectenna. In particular, the RDA offered automatic tracking of the rectenna module in 3D space by employing phase conjugating mixers. The diode rectifier of our rectenna, which is the focus of the present work, offers full-wave-rectification and exhibits a 76% efficiency for an RF input power of 26 dBm and 74% at 27 dBm, while also providing more than 60% of RF-to-DC conversion efficiency at 2.4 GHz when considering an input RF power level ranging from 15 dBm to 29 dBm.

Digital frequency detector based on multiphase ring oscillator

A new high resolution digital frequency detector architecture based on multiphase ring oscillator is proposed, and it uses the time resolution of fast-operating deep sub-micron MOS transistor. The proposed DFD is implemented with 65 nm CMOS technology. The measured frequency resolution is amount to 75 dBc with 10.2 MHz input signal. Fabricated digital frequency detector draws about 4 mA in 1.2 V supply voltage.