Overcoming Parasitics in Sub-28nm Logic Design

Semiconductor design methodology is evolving rapidly as chip complexity increases, process nodes shrink, and time-to-market pressures intensify. Overcoming Parasitics in Sub-28nm Logic Design represents a key aspect of this evolution — a methodology or technology choice that directly impacts design productivity, silicon quality, and manufacturing success.

At INDNIX Technology, our IP and Design division provides design services and IP blocks that embody best practices in Parasitics and related disciplines.

The Design Complexity Challenge

Modern semiconductor designs contain billions of transistors organized into hundreds of functional blocks. Managing this complexity requires rigorous methodology, powerful EDA tools, and extensive verification. The cost of a single tape-out at advanced nodes (28nm and below) exceeds 5 million dollars, making first-silicon success essential — there is no budget for multiple spins.

Parasitics Methodology

Our approach to Parasitics addresses the complexity challenge through several key practices:

Hierarchical Design: Large designs are partitioned into manageable blocks (typically 1 to 10 million gates each) that can be designed, verified, and characterized independently. Block-level sign-off ensures that each block meets its timing, power, and area targets before integration into the full chip.

IP Reuse: Rather than designing every function from scratch, we leverage a library of pre-verified, silicon-proven IP blocks including processor cores, memory controllers, I/O interfaces, analog functions, and communication protocols. IP reuse reduces design time by 30 to 50 percent and eliminates the risk associated with unproven designs.

Early Physical Awareness: Traditional design flows performed logical design first and physical implementation (place-and-route) second, often discovering at the physical stage that the logical design could not meet timing or area targets. Our Parasitics approach brings physical awareness into the earliest stages of design — using floorplan-driven synthesis, physical-aware logic optimization, and early congestion analysis to ensure that logical decisions are physically viable.

FinFET Considerations

The specific technical challenge of FinFET introduces additional design considerations:

Timing and Performance

At advanced process nodes, interconnect delay dominates gate delay. A signal traveling across a chip at 7nm experiences 10 to 100 times more delay in the wires than in the logic gates. This wire-dominated timing environment requires:

• Buffer insertion optimization: Automated algorithms insert thousands of repeater buffers to minimize signal propagation delay through long wires
• Wire sizing: Critical nets are widened to reduce resistance, at the cost of increased capacitance and area
• Layer assignment: Timing-critical signals are routed on upper metal layers (which are thicker and wider) to minimize resistance, while non-critical signals use lower layers
• Clock tree synthesis (CTS): The clock distribution network must deliver clock signals to all sequential elements with skew below 50 picoseconds — requiring carefully balanced H-tree or fishbone clock structures

Power Analysis

Power consumption in modern chips has three components:

• Dynamic power: Proportional to switching activity, capacitance, frequency, and voltage squared. Reduced through clock gating, power gating, and voltage scaling.
• Leakage power: Current that flows even when transistors are nominally off. Increases exponentially with decreasing threshold voltage and increasing temperature. Managed through multi-threshold-voltage (multi-Vt) cell assignment.
• Short-circuit power: Current that flows during switching transitions when both PMOS and NMOS stacks are partially conducting. Minimized through optimized transition times and balanced pull-up/pull-down networks.

Our power analysis flow performs vectorless and vector-based power estimation at every design stage, ensuring that power targets are tracked throughout the implementation process.

Physical Verification

Before tape-out, the design must pass comprehensive physical verification:

• Design Rule Check (DRC): Verifies that all geometric shapes comply with the foundry's manufacturing rules (minimum widths, spacings, enclosures, densities)
• Layout vs. Schematic (LVS): Verifies that the physical layout implements the same circuit connectivity as the schematic netlist
• Electrical Rule Check (ERC): Verifies proper power/ground connectivity, antenna rule compliance, and electromigration current density limits
• Parasitic Extraction: Extracts the resistance and capacitance of every wire and via for accurate timing and signal integrity analysis

Our design flow achieves clean DRC, LVS, and ERC sign-off with zero waivers — ensuring that the GDS-II file sent to the foundry will produce functional silicon.

Sub-28nm and Tools

The choice of Sub-28nm tools and methodologies significantly impacts design productivity and quality:

RTL Design and Verification

• SystemVerilog for RTL design with UVM (Universal Verification Methodology) for functional verification
• Formal verification using property checking and equivalence checking to complement simulation-based verification
• Coverage-driven verification with functional coverage models that track which design scenarios have been exercised

Implementation

• Synthesis: Logic synthesis optimizing for timing, area, and power with multi-corner multi-mode (MCMM) constraints
• Place-and-Route: Automated placement and routing with congestion-driven optimization and detailed routing with via minimization
• Sign-off: Static timing analysis (STA) at all PVT corners, IR-drop analysis under realistic switching patterns, and signal integrity analysis including crosstalk-induced delay effects

INDNIX Design Services

Our IP and Design division offers comprehensive design services:

• Architecture definition: System-level design space exploration and micro-architecture specification
• RTL design: Synthesizable RTL implementation with comprehensive verification testbenches
• Physical implementation: Floorplanning, power planning, place-and-route, and physical verification through tape-out
• Silicon validation: Post-silicon characterization and correlation with pre-silicon simulations

Conclusion

Overcoming Parasitics in Sub-28nm Logic Design is essential knowledge for any team designing complex semiconductor devices. At INDNIX Technology, our design methodology incorporates these best practices into every project, ensuring that our clients' designs achieve first-silicon success with optimal performance, power, and area. Our combination of experienced design engineers, proven IP libraries, and rigorous methodology reduces risk and accelerates time-to-market for even the most complex semiconductor designs.