Crystalline wurtzite zinc oxide (w-ZnO) can be used as a wide bandgap semiconductor for light emitting devices and transparent or high temperature electronics. The use of amorphous zinc oxide (a-ZnO) can be an advantage in these applications. In this paper, we report on x-ray amorphous a-ZnO_x thin films (∼500 nm) deposited at cryogenic temperatures by reactive magnetron sputtering. The substrates were cooled by a nitrogen flow through the copper substrate holder during the deposition. The films were characterized by x-ray diffraction, Raman, infrared, UV–Vis-near-infrared spectroscopies, and ellipsometry. The a-ZnO_x films on glass and Ti substrates were obtained at the substrate holder temperature of approximately −100 °C. New vibration bands at 201, 372, and 473 cm⁻¹ as well as O–H stretch and bend absorption bands in the a-ZnO_x films were detected by Fourier transform infrared spectroscopy. Raman spectra showed characteristic ZnO₂ peaks at 386 and 858 cm⁻¹ attributed to the peroxide ion O₂²⁻ stretching and libration modes, respectively. In addition, the films contain neutral and ionized O₂ and O₂⁻ species. The a-ZnO_x films are highly transparent in the visible light range (≈87%) and exhibit a refractive index of 1.68 at 2.25 eV (550 nm). An optical bandgap is 4.65 eV with an additional band edge absorption feature at 3.50 eV. It has been shown that the deposition on actively cooled substrates can be a suitable technique to obtain low temperature phases that cannot be deposited at room temperature.