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To: Math Junkie who wrote (1951)	2/1/1999 6:38:00 PM
From: Artslaw	Read Replies (1) \| Respond to of 2946

am I correct in assuming that the reason you want higher epsilon is that you're talking about building capacitors I am talking about transistors, but the concept is similar. The current of a transistor is proportional to the gate capacitance of the transistor (it is also roughly inversely proportional to the length, which is the motivation for reducing the channel length). In a DRAM we are concerned about the total charge stored in a cell, which is proportional to the capacitance and cell area. The larger the capacitance, the more charge can be stored (and the less frequently we need to refresh). Of course, DRAM has such low margins that the push is always to shrink the cell area, which reduces the stored charge. The gate capacitance (per unit area) is epsilon/oxide_thickness. Thus, one way to increase the current (for a transistor) or increase the stored charge (in a DRAM cell) is to reduce the oxide thickness OR increase the epsilon. Increasing the epsilon any significant amount requires a material change (i.e. not just SiO2) whereas making the oxide thinner does not (hence is what has been done for a long while). DRAM have an additional constraint for oxide thickness since very thin oxides can leak enough charge further reduces their storage time (and increase the need for refresh cycles). Steve