TSVs-aware Floorplanning for 3D Integrated Circuit
Jieliang Lu
1
, Qin Wang, Jing Xie, Zhigang Mao
School of Microelectronics, Shanghai Jiaotong University, Shanghai 200240, China
Email:wangqin@ic.sjtu.edu.cn
Abstract
3D integrated technique gives a promising method of
overcoming the increasing problems of interconnect wire
length and power consumption. In the design of the
3D-IC, the floorplanning algorithm decides the
performance of the circuit. In this paper, we present a
floorplanning algorithm considering both the critical
wire length and the number of TSVs. Finally MCNC
floorplan circuits are used as benchmarks. The result
shows that the algorithm can reduce the critical wire
length by average 40.1% and reduce the TSVs’ number
by 24.8% under the same critical length. The algorithm
can be widely used in the design of 3D integrated
circuits.
1. Introduction
As wireless communications, automotive electronics
and other consumer electronics products develop quickly,
integrated circuits are facing the great challenges of
multi-functional, compact, portable, high speed, low
power consumption and high reliability. With the
integrated circuit process miniaturization to nano-scale,
the continue development of Moore’s Law becomes
difficult. Three Dimension Integrated Circuit (3D-IC)
makes the modules stacked in the vertical direction. It
also brings heterogeneous integration. Although 3D-IC
still faces with heat dissipation, cost, lack of EDA-tools
and other issues, it is undoubtedly the future direction of
development of electronic systems.
There are several main advantages of 3D integrated
circuit: (1) Reduce the system size. The chips of 3D IC,
which stack up in vertical direction, improve the
encapsulation efficiency significantly, thus reducing the
system size. Compare with 2D encapsulation, 3D
encapsulation can reduce volume 5 to 6 times and reduce
weight 2 to 13 times. (2)Significantly improve system
performance. 3D IC can greatly shorten the interconnect
length. At the same time with reducing chip area,
alleviate delay problems of inter-connect, power, thus
allowing higher speed and lower consumption. (3) Allow
the heterogeneity integration. 3D integrated circuits
provide the possibility of constructing high complexity
system which is mixed a variety of technical devices.
This is the most important advantage of 3D integrated
circuit.
In the 3D-IC technology, vertical interconnection
between the layers mainly uses TSV. With the
development of TSV technology, TSV dimensions
continue to shrink. Now TSV via can be as small as 5
m. For small scale chip, too many TSVs may cost a lot in
the chip manufactory. The result in the paper shows that
a chip with four processors and four 1KB memories in
65nm technique, the area of TSV occupies as much as
43% of the chip. Measures must be taken to reduce the
cost by using fewer TSVs.
In the design flow of 3D-IC, floorplan is one of the
most important steps. It decides the circuit’s structure of
each layer, such as critical length, area, and cost. In this
paper, a floorplanning algorithm is proposed, it can make
the 3D-IC design have a shorter critical wire length and
fewer TSVs. Fewer TSVs mean lower cost. The
algorithm is based on the traditional 2D layout design
and uses the information of the modules as the input of
the algorithm. The floorplan can give the position of
each module in the circuit by using some constrains of
maximum critical wire length and TSV number.
Recent studies on 3D-IC floorplanning algorithm
focused on thermal and performance issues. In [1], the
authors used 3D integration to achieve a fully
functioning multicore processor and memory stacking.
They floorplaned the processors as the bottom layer and
the memory as the top layer. But the authors didn’t
discuss the TSV cost in the design. [2] [3] studied the
TSV modeling and the transmission feature. This helps
us to calculate the delay of TSV. [4] presented about the
interconnect and thermal-aware floorplanning for 3D
microprocessors. [5] showed a multi-layer floorplanning
method for reliable SOP. But the authors didn’t consider
the TSVs either. All these researches did a lot in the
floorplanning method to improve the performance of the
3D-IC, but the cost of using TSV can’t be ignored. In
this paper we give a new floorplan algorithm to short the
critical path of the circuit and using fewer TSVs.
The rest of the paper is organized as follows: Section
2 shows the design flow of the 3D IC and the traditional
floorplan method. Section 3 presents the floorplanning
algorithm. Section 4 presents and discusses our
experimental results. In the last section, we conclude this
paper.
2. 3D Design Flow and Floorplan Method
Because lacking of EDA tools for 3D-IC design,
researchers have to design 3D-IC based on the traditional
2D technique. The design flow is as follows: Frist is
floorplanning. It is to divide the circuit into several
modules and decide which layer and what positions they
are. Then the circuit on each layer is known. The
traditional method can be used to design each layer. Here
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