Tunable Microwave Filters Using HfO₂-Based Ferroelectrics

Area of Science:

• Materials Science
• Electrical Engineering
• Nanotechnology

Background:

• Ferroelectric materials offer tunable dielectric properties crucial for microwave devices.
• Hafnium oxide (HfO2) based ferroelectrics are promising due to their CMOS compatibility.
• Stabilizing ferroelectric phases at room temperature is essential for practical applications.

Purpose of the Study:

• To develop tunable microwave filters utilizing novel ferroelectric thin films.
• To investigate the performance of hafnium zirconate (HfZrO) for tunable microwave applications.
• To demonstrate the feasibility of Atomic Layer Deposition (ALD) for fabricating high-quality ferroelectric films for filters.

Main Methods:

• Fabrication of 6-nm-thick HfZrO ferroelectric thin films using Atomic Layer Deposition (ALD).
• Characterization of film properties including polarization-voltage (P-V) response and surface topography.
• Design, modeling, fabrication, and microwave characterization of low-pass, high-pass, and band-pass filters.

Main Results:

• HfZrO films exhibited stable orthorhombic polar phase at room temperature.
• Tunable frequency response observed for filters with applied DC voltage (0-4 V).
• Filters showed frequency shifts between 90 MHz and 4.4 GHz, with insertion loss as low as 6.9 dB.

Conclusions:

• 6-nm HfZrO ferroelectric thin films enable continuous tuning of microwave filters.
• ALD process provides uniform films with low roughness, suitable for microwave devices.
• The developed filters demonstrate significant frequency tuning capabilities for microwave applications.