## 1 Introduction  
Temperature sensors are widely used in research and industrial applications, such as IC (integrated circuit) chip, micro-resistance temperature detector array [1], and metal cutting [2]. There are four types of commercial temperature sensors: thermocouple, thermistor, resistance temperature detector (RTD), and IC sensor [3]. The thermistor is the only sensor that can be printed as a thin film. NiO is a readily obtained material that is low in toxicity. NiO nanoparticles can be synthesized through several processes, such as the sol-gel and electric arc discharge methods [4; 5]; therefore, over the past few decades, NiO has been frequently used in research concerning gas sensors [6; 7; 8], lactate sensors [9],P-type semiconducting materials [10], supercapacitors [11; 12], catalysts [13], electrodes of battery [14], and resistive switching memories [15]. Additive manufacturing (AM) has been extensively studied [16; 17]; [PERSON] et al. [18] indicated that additive manufacturing (AM) prevented expensive tool-making procedures and increased the efficiency of the manufacturing process. For the thin film fabrication techniques of AM, such as aerosol jet and inkjet, these two printing methods have been applied for printing NiO thermistors in previous studies. NiO is sensitive to temperature variation, which makes it a suitable material for fabricating thermistors. [PERSON] et al. [19] used inkjet to fabricate nickel oxide (NiO) nanoparticle thermistors on flexible substrates. The printed NiO thermistors exhibited good reliability when they were bent, making them suitable temperature sensors for devices with curved surfaces. [PERSON] et al. [20] used aerosol jet printing to print NiO thermistors on three types of turning inserts with different geometric surfaces and successfully achieved high accuracy of measurement of cutting temperatures. The heat treatment of NiO thin films is frequently executed in a furnace [3; 4]. Furnace calcining is a common method for the annealing or sintering of printed thin films [6; 7; 8; 9; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. However, thermal treatment in a furnace is typically time-consuming and can last for several hours [21]. If there are only a few NiO thin film sensors to be heat-treated at a time, it is not economical. Furthermore, there was a phenomenon called necking [22; 23]. It appeared while the energy of sintering or calcination was too large, the adjacent nanoparticles merged into big particles, and the original position of nanoparticles became holes or defects. Therefore, this study analyzed the morphology and strain of UV laser-sintered NiO thin films. Therefore, to improve the efficiency of manufacturing NiO thermistors, laser treatment was used in sintering or annealing NiO thin film sensors. [PERSON] et al. [24] established the optical absorption spectra of NiO nanoparticles, the strongest absorption wavelength of which was approximately 329.5 nm (\(\sim\)3.75 eV), and it was within the UV region (200-400 nm). Based on the research results, this study investigated how UV laser treatment was applied in converting thin films into functional thermistors. [PERSON] et al. applied a continuous wave (wavelength: 514.5 nm) laser to fabricate Ni electrodes by sintering NiO nanoparticle thin films. Through a photothermal reaction of NiO, the agents in the solvent were reduced and the results demonstrated that the Ni thin films had high electrical conductivity and transmittance [25]. [PERSON] et al. modulated the power density and illumination time of the 514.5 nm continuous-wave laser. To analyze the sintering state and mechanism of the photo-physical reductive process of Ni, the study estimated the temporal evolution of transmittance, reflectance, and electrical conductance to establish a diagnostic process as four states: oxidation, reduction, sintering, and reoxidation [22].