Device Coupling Effects of Monolithic 3D Inverters

The device coupling between the stacked top/bottom field-effect transistors (FETs) in two types of monolithic 3D inverter (M3INV) with/without a metal layer in the bottom tier is investigated, and then the regime of the thickness T ILD and dielectric constant e r of the inter-layer distance (ILD), the doping concentration N d (N a ), and length L g of the channel, and the side-wall length L SW where the stacked FETs are coupled are studied. When N d (N a ) ＜ 10 16 ㎝ -3 and LSW ＜ 20 ㎚, the threshold voltage shift of the top FET varies almost constantly by the gate voltage of the bottom FET, but when N d (N a ) ＞ 10 16 ㎝ -3 or L SW ＞ 20 ㎚, the shift decreases and increases, respectively. M3INVs with T ILD ≥ 50 ㎚ and e r ≤ 3.9 can neglect the interaction between the stacked FETs, but when T ILD or e r do not meet the above conditions, the interaction must be taken into consideration.