Conductive metal oxides are interesting for a wide range of applications such as ferroelectric and magnetoresistive devices, solar cells, solid oxide fuel cells (SOFC) and sensors, owing to their excellent chemical and thermal stability. Among the metal oxides, ruthenium dioxide (RuO
2) is particularly interesting since it offers high conductivity (i.e. low specific resistivity, 0.35 µΩm, at room temperature, RT, single crystal, [
1]) and chemical stability. Hence, it is an important material as an electrode for (electro)catalysis (e.g. oxidation reactions, electrolysis,..), energy storage (supercapacitors, Li-ion batteries,..) and semiconductor devices (memristors, gate contacts, [
2]). In capacitor structures RuO
2 electrodes moreover reduce leakage currents, resulting in negligible fatigue and low retention losses, compared to metal electrodes, such as Pt [
3‐
6]. Due to their wide range of applications, RuO
2 thin films have been prepared by a number of techniques such as metal organic vapor deposition (MOCVD) [
7], sputtering [
8‐
11], pulsed laser deposition (PLD) [
12], atomic laser deposition (ALD) [
13,
14] and electrodeposition [
15]. Sol-gel deposition of thin films is cheaper and more flexible compared to the aforementioned physical approaches. However, despite the apparent advantages, there are currently only few reports on the sol-gel preparation of RuO
2 thin films: In 1996 Watanabe et al. prepared RuO
2 thin films by dissolving ruthenium chloride n-hydrate in ethanol and depositing by spin-coating on Si substrates with different annealing temperatures. They obtained a specific resistivity of 1.8 µΩm by adjusting annealing temperature to 800 °C, which led to grain sizes of ~200 nm [
16]. In 1997 Teowee et al. prepared 1 µm thick RuO
2 films with 5 µΩm on silicon substrates, using ruthenium chloride n-hydrate in ethanol [
17]. Yi et al. used Ru nitrosyl nitrate and 2-methoxyethanol to deposit thin films on silicon substrates. They lowered the resistivity of the thin films down to 2 µΩm by increasing the thickness to 450 nm and the low resistivity was almost constant for annealing temperatures between 500 and 700 °C [
18]. In the following year, Yi et al. used the same precursor solution to deposit thin films on stainless steel and achieved lower resistivities with even thinner films (240 nm) [
4]. In 2002, Armelao et al. used dip-coating from alcoholic solutions of Ru(OEt)
3 to prepare thin films and analyzed the thin films using XRD and XPS [
19]. In 1999, Bhaskar et al. used the same components as Teowee et al. to prepare 700 nm thick films with 2.94 µΩm by adjusting the annealing temperature to 700 °C [
20]. To the best of our knowledge, no sol-gel deposition using non-toxic aqueous solutions for the preparation of RuO
2 thin films was reported so far. Such a safe and low-cost approach offers great advantages for industrial applications.