3DCoB: A new design approach for Monolithic 3D Integrated Circuits

H. Sarhan, S. Thuries, O. Billoint and F. Clermidy

CEA-LETI, Minatec Campus, France

ASPDAC 2014

Outline

Introduction Monolithic 3D ICs 3D Cell-on-Buffer (3DCoB) Design Flow Experimental Results Conclusions

Introduction

3D monolithic integration is a methodology to fabricate the 3D IC where a second transistor layer is directly fabricated on top of the first one.

The two transistors layers are connected through high-density inter-tier vias (about 100 times smaller compared to the TSVs).

Monolithic 3D ICs

Monolithic 3D integration approaches: Transistor-level (N/P) Gate-level (Cell on cell)

Transistor-level Gate-level

Monolithic 3D ICs

Transistor-level (N/P)

Gate-level (Cell-on-cell)

3D Cell-on-Buffer (3DCoB)

The main idea of the 3DCoB is to split the non-minimum drive 2D cells into a logical function stage and a drive stage.

One tier contains the equivalent minimum-drive gate.

The other tier contains a buffer to maintain the same driving capabilities of the cell.

The 3DCoB cell has internally two inter-tier vias.

3D Cell-on-Buffer (3DCoB)

3D Cell-on-Buffer (3DCoB)

3D Cell-on-Buffer (3DCoB)

The advantage of the 3DCoB 3DCoB cells can be used by the conventional 2D place

and route tools.

No need for inter-tier routing metal layers between cells.

Improve the overall performance by decreasing the input gate capacitance of the cells.

Design Flow

3DCoB generation process

Design Flow

For example 2-input AND gate (AND2) with drive 42

(AND2x42) Minimum drive for all the 2-input AND gate is 4

(AND2x4) 3DCoB cell will be the min-drive AND2 cell

(AND2x4) connected to the equivalent drive buffer (BUFx42)

Design Flow

Design Flow

Full design flow for 3DCoB approach

Experimental Results

Experimental Results

Experimental Results

Experimental Results

Conclusions

3D monolithic integration technology offers a fine grain integration level thanks to high density and low-parasitics inter-tier vias.

This paper introduced 3DCoB as a new design approach which is fully compatible with the conventional 2D implementation design flow tools.