3. Micro display technology for virtual reality (VR)
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Silicon-based OLED microdisplay refers to a type of flat-panel display made of OLEDs on silicon wafers, and the size is generally less than 1 inch. It uses a mature CMOS technology to make driving circuits on a single crystal silicon wafer, and has the advantages of a wide angle of view, fast response, low power consumption, and all solid state. The fastest response time of the commonly used LCD flip is at 2-4ms, which can cause severe dizziness in VR applications. To solve this problem, head-mounted VR displays must use active light-emitting displays, such as OLED, which greatly reduce the delay time. In fact, Oculus and Valve have used the low afterglow display of AMOLED, while Sony has used its own OLED display. However, most of China’s head-mounted VR use traditional LCD displays, so it is natural to cause dizziness. The modules that need to be designed for this project include source driver, gate driver and pixel circuit. The key and difficult point is to achieve a sufficiently high resolution and refresh rate in a limited size. Because the micro display circuit of each pixel is very small, it needs a large inverse ratio if the MOS transistor is driven in the saturation region, which is a constraint factor to the area, but it is not easy to control if it is driven in the sub threshold region. In addition, the pros and cons of the two driving modes derived from voltage driving and current driving also need to be considered.