The "mirumo 934SH" mobile phone, from Sharp Corp of Japan, is available as part of Softbank Mobile Corp of Japan's summer 2009 line-up. One of the key features of the new handset is the "memory liquid crystal" used in the rear display, which is a monochrome reflective liquid crystal display (LCD) panel with low power consumption (Fig 1). It can constantly display about 30 items provided by Softbank Mobile, including content for time, weather and incoming mail.
High Res 3-Inch DisplayThe memory LCD integrates memory circuits, including static random access memory (SRAM) and dynamic RAM (DRAM), into the pixels of a thin-film transistor (TFT) substrate. Image data is stored to the memory circuits to save power. SRAM, DRAM, etc, are volatile memory, however, so if a given image is displayed for any length of time, it will require periodic image data refresh operations.
Most of the rear displays on existing handsets are about 1-inch monochrome organic light-emitting diodes (OLED). Monochrome OLEDs have relatively high power consumption, about 50mW, and brightness deteriorates over time as the device degrades. These drawbacks have limited image display time to only about 10s or 15s, making it impossible to use them for continuous display as in the 934SH.
The Sharp memory LCD mounted in the 934SH was developed in-house, with a 3-inch screen size and 456 x 240 pixels resolution. Compared to the standard rear display using a monochrome OLED, the screen is larger and the resolution higher. Even better, power consumption is significantly lower. While the actual power consumption figures have not been disclosed, Sharp itself has stated that consumption is "... about 1/500th that of the 0.8-inch monochrome OLED panel in the rear display of the older Sharp 831SH handset." As a result, says Sharp, "It has almost no effect on total handset power consumption even if you leave the information display on continuously."
Integrated SRAM Sharp has not disclosed details of the technology used in the 934SH memory LCD, either. The technology, however, was used in a 1.35-inch prototype shown at FPD International 2008 in Oct 2008, and announced at Society for Information Display (SID) Display Week 2009 (SID 2009), the conference for the display industry, held from the end of May 2009 (Fig 2, Note 1)1).
Note 1: Sharp has also developed a reflective color LCD panel with onboard SRAM. The SRAM has 1 bit each for RGB, providing 8-color display.
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