act as unidirectional valves the preferred third major processing step is to form the heat sink on top of the micro ablation heating element as discussed above a heat sink preferably directs the heat towards the stratum corneum instead of within the bulk silicon material without the heat sink the majority of the heat travels through the silicon because its thermal conductivity is higher than air by depositing an aluminum heat sink on the heater the resulting heat flow is approximately divided evenly between silicon and aluminum this is because the thermal conductivities of both silicon and aluminum are comparable but by selecting a metal with a higher thermal conductivity than that of silicon and aluminum a more efficient heat transfer can be achieved in a preferred embodiment aluminum is used as the heat sink material however additional materials can be applicable in addition to increasing thermal flow towards the stratum corneum the placement of a heat sink preferably reduces the overall distance between the source of heat and the skin barrier thereby reducing power consumption the aluminum is preferably patterned using a lift off procedure however since a thick metal layer may be needed preferably either a thick photoresist is used or the aluminum is deposited over the entire wafer this may cause problems with the metal seal therefore a thin.