Physics / mechanism
High-k dielectrics replace SiO2 as the gate insulator in MOSFETs. SiO2 hit a physical limit ~1.2 nm (direct tunneling leakage becomes unacceptable below ~3 nm equivalent oxide thickness). High-k materials—HfO2 (k≈25), ZrO2 (k≈25), and their silicates/aluminates—allow a physically thicker film to achieve the same capacitive coupling (EOT), suppressing leakage by orders of magnitude. Intel/TSMC adopted HfO2-based gate dielectrics at 45nm (2007). Current nodes use HfO2 + metal gate stacks (HKMG) achieving EOT <0.5 nm at 3nm-class nodes. Interface trap density (Dit) and fixed charge are the key reliability parameters. Doping HfO2 with Si, Al, or La tunes phase stability and EOT.
Competitive landscape
HfO2 also underpins ferroelectric FETs (FeFET): doping with Si, Zr, Y, or La stabilises the orthorhombic phase, enabling non-volatile memory without perovskite complexity. Competing dielectrics include Al2O3 (k≈9, excellent interface, limited capacitance benefit), La2O3/LaAlO3 (higher k, moisture-sensitive, integration difficult), and TiO2 (k>80, severe leakage). For ferroelectric applications, HfO2-based films compete directly with PZT and SBT—legacy perovskites with better Pr but CMOS-incompatible processing. ZrO2 sits at the HfO2/ferroelectric boundary; HZO (Hf0.5Zr0.5O2) is the leading FeFET/FeCAP material.
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Frontier (open questions)
- To be added.