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A Novel Cell Placement Algorithm For Flexible TFT Circuit With Mechanical Strain And Temperature Consideration. Jiun -Li Lin, Po- Hsun Wu, and Tsung -Yi Ho Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan. ASPDAC 2013. Outline.
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A Novel Cell Placement Algorithm For Flexible TFT Circuit With Mechanical Strain And Temperature Consideration Jiun-Li Lin, Po-Hsun Wu, and Tsung-Yi Ho Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan ASPDAC 2013
Outline • Introduction • Initial Static Timing Analysis • Static Timing Analysis with Mobility Consideration • Thermal-aware Non-critical Cell Distribution • ILP-based Critical Cell Distribution • Multilevel Global Placement • Row-based Detail Placement • Experimental results • Conclusion
Introduction • Flexible thin-film transistor (TFT) is the most popular technology used in flexible electronics due to its low fabrication temperature [11], but its performance is severely affected by the mobility variation. • After extensive experiments have been performed , past researches found that TFT’s mobility will be greatly affected by the mechanical strain [4, 5, 10, 12]
Mechanical strain • Mechanical strain is the mathematical expression of the shape changes resulting from mechanical stresses.
Mobility variation • Mobility variation makes a great impact on the cell delay of a flexible TFT circuit which further affects the circuit performance. At worst, mobility variation may leads to timing violation and even function failure. • In addition to the impact of mechanical strain, mobility is also sensitive to temperature change [13, 16].
Initial Static Timing Analysis • All critical cells can be further extracted by backtracking procedure in a manner similar to depth-first search (DFS).
Static Timing Analysis with Mobility Consideration • The static timing analyzer for flexible TFT circuits (STAF) [6] is performed to determine the mobility influence. • STAF only takes the change of mechanical strain into consideration, it is further modified by replacing equation(1) with equation(3) to consider the change of both mechanical strain and temperature.
Thermal-aware Non-critical Cell Distribution • Formulate this problem as a K-way graph partitioning problem to distribute all non-critical cells to different B groups while minimizing total wirelength and the chip temperature.
ILP-based Critical Cell Distribution Exclusivity constraint: Distribution constraint:
Row-based Detail Placement • Initially, it will calculate how many rows can be placed in a bin and partition all cells to different rows based on cell connectivity. • All cells in the same row are classified into hot cells and cool cells, and each cool cell is placed adjacent to the hot cell to reduce the temperature.
Conclusion • The novel cell placement flow and algorithms to minimize the mobility variation caused by the change of both mechanical strain and temperature while minimizing total wirelength.