A Low-Power Memory-in-Pixel Circuit for Liquid Crystal Displays Comprising Low-Temperature Poly-Silicon and Oxide Thin-Film Transistors

Jongbin Kim,Hoon-Ju Chung,Seung-Woo Lee,Woo-Rim Lee

doi:10.3390/electronics9111958

Abstract

In this paper, a new pixel structure using low-temperature polycrystalline silicon and oxide (LTPO) thin-film transistors (TFTs) for low-power liquid crystal displays (LCDs) is proposed. The extremely low off-state current of oxide semiconductor TFTs enables the proposed circuit to operate at a very low frame frequency of 1/60 Hz, so that the power consumption can be significantly reduced. In addition, the low-temperature polycrystalline silicon TFTs with high reliability directly drive pixels, which can achieve stable and flicker-free LCDs. The proposed circuit is fabricated using the LTPO TFT backplane and successfully verified by simulation and measurement results. The measurement results prove that the proposed circuit operates well without further programming for 60 s, and the power consumption in the panel (except backlight power) can be reduced to 0.02% of that of conventional LCD.

Highlights

Mobile electronic devices such as laptop and tablet computers, smart phones, and smart watches require displays with high resolution and low power consumption [1,2]
A new thin-film transistor (TFT) backplane technology has been employed in mobile display products, so called low-temperature polycrystalline silicon and oxide (LTPO) thin-film transistors (TFTs) technology
LTPO TFTs were mainly used in complementary metal oxide semiconductor (CMOS) inverter circuits [3,4]

Summary

Introduction

Mobile electronic devices such as laptop and tablet computers, smart phones, and smart watches require displays with high resolution and low power consumption [1,2]. The objective of the MIP circuit was to integrate the memory devices into the pixel area Based on this motivation, many studies to reduce the power consumption of display panels were undertaken for several years [13,14,15,16,17,18]. Kimura et al [13] developed a reflective LCD with an MIP circuit They added a digital memory circuit to the conventional LCD pixel structure based on LTPS TFT backplane. Tamaki et al [16] developed an MIP circuit which embeds SRAM circuits in each pixel for reflective-type LCD based on LTPS TFTs. The reflective-type LCDs with their proposed MIP circuit has been commercialized for various display applications such as digital signage, smart watches, and electronic shelf labels.

Review of Memory Cell Comprising LTPO TFTs

Proposed Pixel Circuit

Results

Discussion

Conclusions