Zinc oxide (ZnO)

Zinc oxide (ZnO) is a wide‑bandgap (~3.3 eV) n‑type semiconductor that combines high visible transparency, decent carrier mobility, chemical stability, and notable piezoelectricity, while being abundant and non‑toxic. It is readily deposited by magnetron sputtering for uniform, large‑area films and by atomic layer deposition (ALD) for ultra‑conformal, low‑temperature coatings on complex, high‑aspect‑ratio structures. As a transparent thin film, ZnO serves as a window/contact in photovoltaics and LEDs and as a transparent electrode when adequately doped or hydrogenated to lower sheet resistance. In optics and photonics, ZnO functions as a high-index, low-loss dielectric for waveguides, tunable anti-reflective coatings, and Bragg mirrors; its stoichiometry and carrier density allow for control of the refractive index and absorption. Its piezoelectric and surface‑active nature underpins surface‑acoustic‑wave devices, microphones, nanogenerators, and highly responsive UV and gas sensors. Beyond these, polycrystalline ZnO varistors are standard for surge protection, and patterned or hybrid ZnO stacks enable transparent heaters, low-emissivity/IR-control, and EMI-shielding coatings, while offering good hardness and corrosion resistance.

Deposition of ZnO

ZnO can be deposited by the Sputtering process and atomic layer deposition (ALD). In the chart below, you can compare the different deposition equipment.

	Sputtering deposition (Lesker)	Atomic layer deposition (ALD Picosun R200)
General description	Sputter deposition of ZnO	Atomic layer deposition of ZnO
Pre-clean	RF Ar clean
Layer thickness	10Å to 5000Å*	0 to 1000 Å
Deposition rate	Depending on process parameters.	Depending on temperature
Batch size	Pieces or 1x4" wafer or 1x6" wafer	Pieces or 1x4" wafer or 1x6" wafer or 1x8" wafer
Allowed materials	Silicon Silicon oxide Silicon nitride Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals Carbon	Silicon Silicon oxide, silicon nitride Quartz/fused silica Al, Al₂O₃ Ti, TiO₂ Other metals (use dedicated carrier wafer) III-V materials (use dedicated carrier wafer) Polymers (depending on the melting point/deposition temperature, use carrier wafer)
Comment	Use 2 inch target Substrate rotation Substrate RF Bias (optional)

* For thicknesses above 200 nm permission is required.