Through-Silicon Vias (TSVs): Interconnect Basics, Design Rules, and Performance

Through-silicon vias (TSVs) are one of the foundational enablers of modern three-dimensional integrated circuit (3D-IC) technology, providing vertical interconnects that cut through the silicon to connect stacked dies with short, low-latency signal paths. In this blog post, we dive into the structure, pitch, and electrical behavior of TSVs, explain key layout rules such as keep-out zones (KOZs) and stress constraints, and explore how TSV parasitics influence bandwidth, latency, and system-level performance.

The first part of the post introduces essential concepts, including TSV pitch, TSV parasitics, stacked dies, advanced packaging, hybrid bonding, interposers, micro-bumps, and TSV reliability. These topics collectively provide a solid foundation for understanding the role of TSV-based integration in modern 3D-IC design and the associated architectural tradeoffs.

TSV Structure, Pitch, and Electrical Behavior

A TSV is fundamentally a vertical metal plug, usually copper embedded through the thickness of a silicon die. The classic fabrication flow includes deep reactive-ion etching (DRIE), liner and barrier deposition, copper electrochemical deposition, and backside thinning to expose the vias. Depending on when the via is introduced in the process flow, TSVs are categorized as via-first, via-middle, or via-last, with via-middle being the most widely adopted for high-density logic-memory stacks.

TSV Pitch and Density

Source MIT LL

TSV pitch is a critical parameter that directly affects system design choices. A tighter pitch enables more vertical interconnects per unit area, supporting higher bandwidth between stacked dies. However, reducing pitch increases several challenges:

• Higher parasitic coupling between adjacent TSVs
• Greater mechanical stress due to dense metal insertion
• Larger aggregate KOZ regions that reduce placement flexibility

As a result, TSV pitch selection becomes a joint optimization of electrical performance, mechanical reliability, and physical design constraints.

Electrical Parasitics

TSVs behave as complex three-dimensional structures, and their parasitics—resistance, capacitance, and inductance—must be accurately modeled early in the flow. These parasitics influence signal integrity, timing closure, power delivery, and cross-tier communication.

• Capacitance: A TSV acts as a metal-insulator-semiconductor capacitor. Higher TSV capacitance can increase delay, degrade noise margins, and introduce crosstalk into nearby nets. The capacitance is driven by the via diameter, oxide thickness, and substrate properties.
• Resistance: Copper fill resistance becomes non-negligible for high-frequency signals. For wideband memory and high-speed SerDes paths, TSV resistance directly influences insertion loss and power-per-bit efficiency.
• Inductance: The vertical geometry of TSVs can introduce noticeable inductive behavior for fast edges and GHz-range components, affecting impedance matching and eye margins.

For all of these reasons, TSV parasitics must be incorporated into early EM-aware planning, something Cadence’s Integrity 3D-IC Platform supports through integrated multiphysics analysis and unified stack parasitic modeling.

Layout Considerations: Keep-Out Zones and Stress Effects

TSV insertion dramatically reshapes the physical layout of a die. Unlike metal interconnects that reside in BEOL layers, TSVs cut vertically through active silicon—requiring strict layout rules.

Keep-Out Zones (KOZs)

Every TSV requires a keep-out zone, an exclusion region where no active devices or sensitive interconnects can be placed. KOZs are essential to prevent doping distortions, mobility degradation, leakage shifts, and stress-induced transistor performance variation. The TSV KOZ size is typically influenced by TSV diameter and pitch, process node, and substrate mechanical properties. In Cadence design flows, the KOZ regions are automatically created during TSV generation, with placement blockages inserted so that standard cells and routing remain outside the constraint boundaries.

Stress and Mechanical Reliability

Copper has a higher coefficient of thermal expansion (CTE) than silicon. During temperature cycling—whether during fabrication, bonding, or operation—copper expands and contracts differently from the surrounding silicon. This induces localized stress, which can shift transistor characteristics, cause delamination or cracking, increase timing variability, and impact long-term reliability.

To mitigate these stress effects:

• Ground or pseudo- TSVs may be inserted as stress buffers
• TSV placement is spread to reduce localized hotspots
• Thermal-aware floor plans distribute heat-generating blocks away from TSV clusters.

Mechanical and thermal simulations—supported by the multiphysics capabilities of the Integrity 3D-IC Platform—are crucial for validating stack viability before committing to manufacturing.

Bandwidth and Latency Implications vs Micro-Bumps

TSVs are often compared to micro-bumps, especially in the context of 2.5D interposer designs and conventional die-to-die bonding. The fundamental advantage of TSVs is the much shorter vertical path length, typically tens of microns compared to hundreds of microns for micro-bumps.

Bandwidth

• TSVs enable significantly higher vertical bandwidth density because they support more parallel connections in a smaller footprint.
• Memory stacks such as high bandwidth memory (HBM) rely on dense TSV arrays to achieve multi-Tb/s bandwidth per stack.
• Micro-bumps remain viable for chiplet-style interfaces across interposers but cannot match TSV density for true vertical stacking.

Latency

• TSVs provide lower interconnect latency due to their short path length and reduced RC delay.
• Micro-bump interconnects introduce longer paths and additional parasitic layers, increasing latency for high-performance compute workloads.

Thermal Considerations

TSVs can double as thermal conduits, helping extract heat vertically—micro-bumps do not provide the same thermal advantage. However, TSVs also introduce thermal stress, requiring balanced placement strategies.

TSV Budgeting in Early Stack Planning

Engineering teams must determine their TSV budget early in the 3D-IC planning phase. This number influences die size, partitioning strategy, bandwidth goals, and overall package economics.

Key budgeting considerations include:

• Signal TSVs: For memory channels, cross-tier nets, and wide datapaths
• Power TSVs: For vertical power delivery networks
• Thermal TSVs: For heat extraction in high-power logic stacks
• Redundancy TSVs: For yield enhancement and reliability

Cadence’s Integrity 3D-IC Platform workflow supports hierarchical planning, enabling architects to experiment with TSV counts, pitches, and placements while simultaneously analyzing thermal, electrical, and mechanical impacts. Early co-design between die, interposer, and package helps avoid costly ECO cycles later.

Verification and Reliability Concerns for TSVs

TSV-based architecture introduces verification requirements that differ significantly from 2D-IC design.

Electrical Verification

• Accurate parasitic extraction of TSV arrays
• Timing analysis incorporating cross-tier paths
• SI/PI analysis for vertical power networks
• EM-IR validation for TSV-intensive regions

Physical Verification

• Rule checking for KOZ overlap
• Minimum spacing between TSVs and active circuitry
• Alignment verification across stacked dies
• Layer-to-layer connectivity checks

Reliability Verification

TSVs bring long-term reliability considerations such as:

• CTE-induced fatigue
• TSV liner cracking
• Copper pumping
• Stress migration

Cadence’s multiphysics engines help engineers perform thermo-mechanical reliability checks within a unified environment, reducing fragmentation across EDA tools.

Hybrid Bonding vs TSV: When to Use Which

Hybrid bonding and TSVs are complementary, each valuable in specific design contexts.

Use Hybrid Bonding When:

• Ultra-fine pitch is required (<10 µm)
• Highest interconnect density and lowest parasitics are needed
• Routing flexibility between tiers must be maximized
• Power-per-bit is a priority for AI accelerators and HPC logic stacks

Use TSVs When:

• Thicker silicon needs to be traversed
• High thermal conductivity is beneficial
• Power delivery needs vertical routing
• Memory stacking (e.g., HBM) requires high bandwidth density
• 2.5D interposers need pathways to the package substrate

Hybrid bonding excels in logic-logic stacking. TSVs are essential for logic-memory integration, interposer-based 2.5D structures, and power delivery.

Request a Design Assessment or Demo

If your team is exploring 3D-IC integration, you can request a design assessment to review stack feasibility, interposer requirements, and potential multiphysics risk areas. This collaborative evaluation helps identify where the Integrity 3D-IC Platform can improve integration efficiency, modeling accuracy, and time to signoff, giving your project a stronger foundation from the start.

• Explore the Cadence Multi-Die 3D-IC Solution to see how Cadence empowers next-generation system innovation.
• Explore the Integrity 3D-IC Platform to discover how 3D design and signoff enable system-level optimization.
• Talk to a 3D-IC Specialist to discuss your design challenges and roadmap.

Read More

• What Is 3D-IC Technology? Fundamentals, Architecture, and Design Concepts
• 3D-IC Design Tools: Cadence Workflows for Planning, Assembly, and Analysis
• 2.5D vs 3D-IC: Architecture Tradeoffs, CoWoS Examples, and a Practical Selection Guide