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LTPO – LTPS with Minimum Off Current, VRR and 15+ Masks
Samsung raised the stakes in the high profit, high end smart phone panel world, by implementing LTPO, combination of an LTPS TFT switch and a IGZO TFT driver for current. The combination of P-LTPS and n-IGZO, allows the driver to use less power by minimizing refresh steps for sub-pixels that don’t change. Sharp presented at DisplayWeek and their version of the circuit including showed:
Figure 1: Simple LTPO Pixel Circuit
Samsung raised the stakes in the high profit, high end smart phone panel world, by implementing LTPO, combination of an LTPS TFT switch and a IGZO TFT driver for current. The combination of P-LTPS and n-IGZO, allows the driver to use less power by minimizing refresh steps for sub-pixels that don’t change. Sharp presented at DisplayWeek and their version of the circuit including showed:
- Combination of p-LTPS and n-IGZO
- IGZO TFTs for low refresh rates T1 and T2
- High refresh rate driving, were
- pScan delay affects the driving speed
- T7 is driven by EM instead of pScan to reduce the load on pScan
Figure 1: Simple LTPO Pixel Circuit
Sharp create a number of iterations of the pixel circuit as shown below. They tried a combination of p-LTPS and n-IGZO, which was simpler driving circuit to minimize the # of TFTs
Figure 2: Refined LTPO Pixel Circuit
Figure 2: Refined LTPO Pixel Circuit
Figure 3: Hybrid TFT Structure
Figure 4: TFT Characteristics on OLED Panel
Figure 4: IGZO and LTPS TFT Characteristics
Figure 5: IGZO Process Optimization and Reliability
Figure 6: On Margin: Panel Reliability
The number of fabs being converted to LTPO is shown in the next table and it is likely that due to the additional masks and equipment, capacity could be reduced by up to 20% per fab.
Table 1: LTPO Planned Conversions
Table 1: LTPO Planned Conversions
