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In this paper, we investigate the impact of Tox and Vth on power performance trade-offs for on-chip caches. We start by examining the optimization of the various components of a single level cache and then extend this to two level cache systems. In addition to leakage, our studies also account for the dynamic power expended as a result of cache misses. Our results show that one can often reduce overall power by increasing the size of the L2 cache if we only allow one pair of Vth/Tox in L2. However, if we allow the memory cells and the peripherals to have their own Vth and Tox, we show that a two-level cache system with smaller L2s will yield less total leakage. We further show that two Vth and two Tox are sufficient to get close to an optimal solution, and that Vth is generally a better design knob than Tox for leakage optimization, thus it is better to restrict the number of Tox rather than Vth if cost is a concern.