## 1 Introduction  
Zinc oxide (ZnO) is a group II-VI compound semiconductor with excellent semiconducting properties [1]. It has been widely used for the making of opto-electronic devices such as light emitting diodes [2], laser diodes [3], gas sensors [4], biosensors [5], solar cells [6] and display applications [7]. This is because of its unique properties, i.e., low cost, non-toxic, wide band gap (3.37 eV) and large exciton binding energy (60 meV) at room temperature [8]. Moreover, the optical and electrical properties of ZnO films could be easily tailored via dopants such as Au [9], Co [10], Cd [11], Na [11], F [12] and Ba [13], Mg [13] and Ni [14]. Thus, ZnO films remain as one of the semiconductor materials preferred by researchers for the making of opto-electronic devices since the 1990s. Various techniques have been developed to deposit ZnO films on substrates. These includes sol-gel [15], hydrothermal [16, 17], dip-coating [18], sputtering [19], chemical vapour deposition (CVD) [20], atomic layer deposition (ALD) [21] and pulsed laser deposition (PLD) [22] as listed in Table 1. The properties of the ZnO films obtained differ according to the deposition technique used such as film thickness, morphology, and electrical properties. For instance, [PERSON] et al. used doctor blade to deposit ZnO thin films and reported a transparency reduction with increasing film thickness [23]. [PERSON] et al. reported that low sheet resistance of ZnO film enhanced the rate of sensitivity to light [24]. [PERSON] and co-workers concluded that high hydrogen content increased the electron concentration and reduced sheet resistance of ZnO films [25]. Using the sol-gel method, [PERSON] et al. reported that the bandgap decreases with thicker ZnO film layer obtained through repetitive coating [26]. [PERSON] and co-workers reported that ZnO films deposited using the SILAR method, mesoporous structures can be obtained, which acted as barriers that could prolong the recombination of charge carriers [27]. The abovementioned deposition techniques are either obtained using sophisticated high-cost equipment or time-consuming processes. Aerosol deposition (AD) is a potential rapid deposition technique for thin and thick film fabrication. The advantage of the AD method is the feasibility to obtain a consolidated film deposition through a room temperature impact consolidation (RTIC) process [29]. The RTIC phenomenon has been described by [PERSON] where consolidation of ceramic powders exhibiting strong bonds and finer crystal grains at room temperature due to shock compaction. The collision of the particles with a substrate would generate high impact shock leading to formation of finer crystal grains and particle bonding. Localized heating at the particles' interface during collision and compaction could promote the bonding between particles. Various research works have been performed by researchers using the AD method for different applications. For examples, the effect of particles' kinetic energy and particle-substrate relative hardness ratio on anchor layer formation during AD were investigated by [PERSON] et al. [30], they then further demonstrated the feasibility to control the optical properties of the AD films in the ultraviolet and infrared region using electrostatically assembled composite particles Thick films of BaTiO\({}_{3}\) were produced using AD by [PERSON] et al. exhibiting improved dielectric properties that can be used at moderate temperature condition (approximately 500 \({}^{\circ}\)C) without the need of post-sintering [31]. The hardness and Young's modulus of BaTiO\({}_{3}\) films deposited by [PERSON] et al. using the AD method were improved by increasing the film thickness [32]. The PbTiO\({}_{3}\) films synthesized by [PERSON] et al. [33] on stainless-steel substrate by the AD method exhibited a good ferroelectric behaviour.