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**Exploring 3D Power Distribution Network Physics**

Xiang Hu1, Peng Du2, and Chung-Kuan Cheng2 1ECE Dept., 2CSE Dept., University of California, San Diego 10/25/2011 1

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**Outline Introduction 3D power distribution network (PDN) model**

Circuit model Current model 3D PDN analysis flow Experimental results On-chip Current Distribution Resonance phenomena Noise reduction techniques Larger decap around TSVs Reduce Tier to tier impedance Conclusions

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**Introduction Power delivery issues in 3D ICs Coarse power grid models**

More tiers => More current Same footprint on package TSVs and µbumps between tiers Coarse power grid models Missed detailed metal layer information Current source models Detailed 3D PDN analysis Frequency domain: resonance behavior Time domain: worst-case noise

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**3D PDN Circuit and Current Models**

Circuit Model Lump model: Two-port model for chip between tiers Fine grid model: all metal layers: m1+ Current Model Power law Phase in f domain

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**3D PDN Distributed Model[1]**

Power grid Structure: M1, M3, M6, RDL Each layer extracted in Q3D T2T: TSV+μbump Modeled as an RLC element Package: C4 bump based RLC model [1] X. Hu et al., “Exploring the Rogue Wave Phenomenon in 3D Power Distribution Networks,” IEEE 19th Conf. on Electrical Performance of Electronic Packaging and Systems, Oct. 2010, pp. 57–60.

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**Frequency-Domain Current Stimulus Model**

Noise depends on the current model Rents rule power law: P: power consumption A: area k: constant number γ: exponent of the power law Current configurations γ =0: single current load 0< γ <1: taper-shaped current distribution γ =1: uniform current distribution In f domain, we can tune the phase

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3D PDN Analysis Flow

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**Experiment Base Setup Two-tier PDN**

TSV setup: 3x4 TSVs connected to M1 and AP on both side 5nF/mm2 decap on T1; 50nF/mm2 decap on T2 2x2 C4 on T1 AP Per bump inductance: 210pH Per bump resistance: 18.7mΩ M1 M3 M6 AP TSV T1 T2 Pitch (um) Width (um) X step Y step 2.5 0.2 8.5 0.25 30 4 400 3 20 40

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**Current Model: Input on T1**

Two-tier PDN + VRM, board, and package Decap: Current: T1; distr.(γ=0, 0.5, 1) Probe A: T1 TSVs B: T1 between TSVs C: T2 Observation Smaller γ => larger noise Resonance at non-TSVs, but not at TSVs brd-pkg T1-T2 VRM-brd

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**Current Model: Noise Map w/ Input on T1 (@1GHz)**

γ=0 γ=0.05 γ=1 T2

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**Current Model: Input on T2**

Two-tier PDN + VRM, board, and package Decap: Current: T2; distr.(γ=0, 0.5, 1) Probe A: T1 TSV location B: T1 non-TSV location C: T2 Observation Smaller γ => larger noise

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**Current Model: Noise Map w/ Input @T2 (1GHz)**

γ=0 γ=0.05 γ=1 T1 T2

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**Resonance Phenomena Decap: 5nF/mm2 @T1; 50nF/mm2 @T2**

Current: T1 or T2, unif. (γ=1) Observation: resonance vary with decap configurations Probe: T1 Current: T1 Probe: T2 Current: T2 Global mid-freq resonance non-TSV locations. From lumped model: No mid-freq resonance peak due to “Rm1” No resonance TSV locations

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**Decap: Larger Decap Around TSVs**

Decap: Case 1: uniform Case 2: half of decap at Observation: Case 2 is better Probe: T1 between TSVs Current: T1 unif. Probe: T2 Current: T2, unif Probe: T2 Current: T1 unif

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**Tier to Tier Impedance: Number of TSVs**

TSV Setup Setup Case 1 Case 2 Case 3 TSV X step (M1 segments) 40 20 15 TSV Y step (M3 segments) 100 18 # TSV 4 12 32

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**Tier to Tier Impedance: Number of TSVs**

TSV(Xpitch,Ypitch) Case 1: (40, 100) Case 2: (20, 40) Case 3: (15, 18) Current: T1, unif. (γ=1) Probes A: T1 TSV B: T1 between TSVs C: T2 Observation noise drops as #TSV increases resonance f drops as #TSV increases Resonant f determined by Cd1 As T2T impedance becomes smaller, resonance frequency is determined by both Cd1 and Cd2

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**On-chip power network model Current distribution model **

Conclusion On-chip power network model Current distribution model Power law current distribution model reflects the current-area relation Decap: Various on-chip resonances Techniques of reducing 3D PDN noise Larger decap around TSV area Small tier to tier impedance

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Thank You! Q & A

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