monolithic

**Monolithic 3D VLSI Integration** is **stacking multiple device layers on silicon via sequential processing for extreme integration density** — achieves 3-4x density gain. Monolithic 3D transcends 2D planar limits. **Sequential Processing** grow first layer, insulate, pattern vias, repeat for next layer. Layer-by-layer construction enables vertical integration. **Thermal Budget** second layer processing limited by first layer (interconnects stable to ~500°C for copper). Requires lower-temperature processes for upper layers. **Channel Material Quality** regrown silicon via solid-phase crystallization or transfer maintains crystallinity. **Device Stacking** stack transistors vertically. Significant footprint reduction. **Interlayer Connections** vias through dielectric connect layers. Contact/via resistance critical. **3D Density** theoretical 3x improvement; practical 2-2.5x accounting for overhead. **Prototype Status** demonstrated by MIT, Samsung on research circuits. Not yet production volume. **Power Efficiency** shorter interconnects reduce capacitance, power dissipation. **Thermal Management** lower tiers' heat dissipates through upper layers, challenging. **Stress Control** CTE mismatch between materials; engineering mitigates via films. **Gate Engineering** gate-last compatible with sequential processing. **Yield Challenges** first-tier defects propagate; yield lower than 2D. **Monolithic 3D achieves maximum density** through stacked sequential processing.