Low-Voltage High-Speed Ring Oscillator with a-InGaZnO TFTs (original) (raw)
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A Comparitive Study of On-Chip Clock Generators Using a-IGZO TFTs for Flexible Electronic Systems
2018 International Flexible Electronics Technology Conference (IFETC)
This paper presents a comparitive study of ring oscillators (RO) using amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs) to implement on-chip clock generator for flexible electronic systems. A five-stage RO has been implemented with different inverter topologies using IGZO TFTs, which includes Diode connected load, Capacitive bootstrapping (BS), Pseudo-CMOS and Pseudo-CMOS bootstrapping architectures. These topologies have been simulated using in-house IGZO TFT models under similar conditions using different power supplies (10 V, 15 V and 20 V) in cadence environment. Among all architechtures Capacitive bootstrapping RO has ensured highest frequency of operation in the order of MHz and an output swing of 82% of VDD. Whereas, Pseudo-CMOS based RO provides the lowest power consumption in the order of µW with an output swing of 57% of VDD. On the other hand, the combination of Pseudo CMOS and bootstrapping has ensured highest voltage swing of 95% of VDD. In terms of power delay product (PDP) BS RO is superior with respect to other topologies. This work provides a clear insight to the designer to choose a particular topology for given application, mainly for onchip clock generation for flexible electronic systems based on the requirements.
A Voltage Controlled Oscillator Using IGZO Thin-Film Transistors
2018 IEEE International Symposium on Circuits and Systems (ISCAS), 2018
This paper presents a voltage controlled oscillator (VCO) using amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs). This circuit consists of a high-gain OpAmp, a comparator and a relaxation oscillator. The implemented relaxation oscillator shows a power consumption of 700 μW, when it is simulated with a supply rail of ±5 V. It shows a frequency of oscillation range from 327 to 560 Hz, when the tuning capacitance value varies from 1.6 to 5 pF. On the other hand, the VCO has a power dissipation of 1.3 mW with frequency ranging from 400 to 556 Hz with a controlling voltage from −5 to 5 V. In-house oxide TFT model is used for circuit simulations in Cadence environment. This circuit finds potential applications in large-area flexible systems, namely smart packaging, biomedical and wearable systems, which needs clocks with different frequencies.
Circuits using uniform TFTs based on amorphous In-Ga-Zn-O
Journal of the Society for Information Display, 2007
High-performance and excellent-uniformity thin-film transistors (TFTs) having bottom-gate structures are fabricated using an amorphous indium-gallium-zinc-oxide (IGZO) film and an amorphous-silicon dioxide film as the channel layer and the gate insulator layer, respectively. All of the 94 TFTs fabricated with an area 1 cm 2 show almost identical transfer characteristics: the average saturation mobility is 14.6 cm 2 /(V-sec) with a small standard deviation of 0.11 cm 2 /(V-sec). A five-stage ring-oscillator composed of these TFTs operates at 410 kHz at an input voltage of 18 V. Pixel-driving circuits based on these TFTs are also fabricated with organic light-emitting diodes (OLED) which are monolithically integrated on the same substrate. It is demonstrated that light emission from the OLED cells can be switched and modulated by a 120-Hz ac signal input. Amorphous-IGZO-based TFTs are prominent candidates for building blocks of large-area OLED-display electronics.
Ring oscillators: Characteristics and applications
Indian Journal of Pure and Applied …, 2010
The structure and operating principle of ring oscillators (RO) have been described. The expression for the frequency of oscillation of a complementary metal oxide semiconductor (CMOS) delay cell based conventional ring oscillator is presented and propagation delay of the delay stages is calculated. The limitations of a conventional RO have been studied and a few techniques to overcome these limitations have been mentioned. In this context, some modified structures of ring oscillators such as negative skewed delay RO, multi feedback RO, coupled RO are described for high frequency oscillation. The effect of noise sources on the output of ring oscillators has also been studied. Some potential applications of such ring oscillator based on its voltage tuning characteristics and multiphase outputs are also mentioned.
An Improved Performance Ring Oscillator Design
2012
This paper presents a new technique to improve frequency performance of CMOS ring oscillator. It is based on the addition of MOS transistor to boost switching speed of the oscillator delay cell. The method can be used for simple and differential oscillator and offers a simple way to implement frequency tuning without introduction of any additional phase noise. Using 0.35 μm CMOS technology, simulation results show that applying the technique to the simple ring oscillator allows a frequency oscillation improvement of 80%. Also, simulations show that frequency improvement can reach 300 % if the technique is associated to a positive feedback.
High-Speed and Low-Voltage-Driven Shift Register With Self-Aligned Coplanar a-IGZO TFTs
IEEE Electron Device Letters, 2000
We report a high-speed and low-voltage-driven shift register utilizing self-aligned coplanar amorphous-indiumgallium-zinc-oxide thin-film transistors (a-IGZO TFTs). The a-IGZO TFTs exhibit field-effect mobility, threshold voltage, and gate-voltage swing of 24.7 cm 2 /V • s, 0.2 V, and 118 mV/dec, respectively. The rise and fall times of the shift register at the supply voltage (V DD) of 1 V are 8 and 7 μs, respectively, and the output pulse is free from distortion or ripple. For a V DD of 15 V, the clock frequency of the shift register approaches 500 kHz, making it applicable to high-resolution active-matrix displays. Index Terms-Amorphous-indium-gallium-zinc-oxide (IGZO) (a-IGZO) thin-film transistor (TFT) (a-IGZO TFT), coplanar, low-voltage driven, self-aligned process, shift register.
Analysis of frequency dispersion in amorphous In–Ga–Zn–O thin-film transistors
It is shown in this paper that the finite resistance of the accumulation channel in amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) is the main cause of the frequency dispersion of the capacitance-voltage curves in these devices. A transmission line model, accounting for the distributed nature of channel resistance, is used to explain this. Multi-frequency analysis techniques for trap density distribution use a lumped series resistance model and attribute dispersion solely to the charging and discharging of trap states. As the resistance-capacitance (RC) time constant values of the IGZO TFTs are in the range of 10-100 μs, a distributed RC network is better suited for the measured frequency range (1 kHz-1 MHz).
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2006
The operation of a CMOS ring oscillator with supply voltage values as low as ~80 mV are experimentally investigated. The low-voltage operation of the ring oscillator based on a single inverter, is analyzed. The use of body voltage of MOS transistors as a means for controlling the frequency of oscillation of CMOS ring oscillators are demonstrated. The feasibility of very low-voltage operation of logic CMOS gates such as NAND gate is confirmed with simulation.
A ring oscillator based on HIFETs
Organic Electronics, 2012
A hygroscopic insulator field-effect transistor (HIFET) ring oscillator with three inverters was built and tested under ambient laboratory conditions. An operating voltage of À2 V was used, yielding a peak-to-peak output voltage of 1.1 V and an oscillation frequency of 28 mHz. For Spice (simulation program with integrated circuit emphasis) simulation of the HIFET circuits the measured HIFET output characteristics were fitted to a DC (direct current) model and additional measurements were made to find the magnitude of the capacitive and resistive elements in the HIFET gate structure. The results indicated that HIFETs have a good potential for use in amplifier and sensor circuit applications where high operation speed is not crucial.
Effect of Insulators on the a-IGZO TFT Performance
University of Maribor Press, 2017
Indium Gallium Zinc Oxide (IGZO) thin films have attracted significant attention for application in thin-film transistors (TFTs) due to their specific characteristics, such as high mobility and transparency. The performance a-IGZO thin film transistors (TFTs) with four different insulators (SiO2 Si3N4, Al2O3 and HfO2) are examined by using numerical simulation. It is found that the output performance is significantly enhanced with high relative permittivity of the insulator. The HfO2 gate insulator gives the best performance: lower threshold voltage and subthreshold, and higher field effect mobility, on current and Ion/Ioff ratio.