Study Of Direct Inkjet Printing Technology For ZnO Ultraviolet Sensor Based On MEMS Technology

In recent years, Micro Electronic Mechanical System(MEMS) field has gradually become intelligent, customized, integrated and flexible. Most scholars have shifted their attention to the study of direct-writing technology for the special need of the production process. Direct inkjet printing technology is one relatively mature form among direct-writing technology, which features as an off-contact technology that deposits functional ink in the predesigned patterned array known as the overlapped dot matrix. It is based on ejection of fluid droplets from a nozzle directly to a pre-specified position controlled by computer. Therefore, it is a digital, rapid prototyping and low cost without extra mask process.It is well known that ZnO is a light-sensitive material with 3.37 eV band gap and large exciton binding energy of 60 meV. As this material can be prepared as ink for the direct inkjet printing system, it is made into a low-cost ultraviolet sensor. This kind of sensor is highly useful and applied to many areas in daily life, such as detecting the ultraviolet which is beyond body sensory and switches for photoelectric control. Here we propose a novel low-cost and environmental-friendly ZnO sensor fabricated on paper substrate to detect UV based direct inkjet printing technology. Low cost and widely used paper is used as the substrate of our sensor. Water suspension of ZnO nanoparticile is deposited by direct inkjet printing technology as sensing part of our sensor. Low cost graphite is used as the electrode of our sensor.Main works in this paper are concluded:1) Firstly, we reviewed and compared several mainstream fabrication technology, and briefly introduced their principle followed with typical pattering structure. Between them, two methods, continuous inkjet printing and drop-on-demand inkjet printing, are most commonly used. As drop-on-demand inkjet printing method is more mature, we here utilized this method for our ZnO UV sensor.2) Moreover, we carried out an insight review on material selection and critical printing parameters for different printable inks. As a result, we found the biggest challenge for direct inkjet printing technology is the preparation of printable functional ink.3) After that, experiments of ZnO ink preparation, surface characterization of the paper substrate, and low-cost graphite electrodes which act as the electrode of the sensor were done.4) After fabrication, paper, graphite pencil line and ZnO thin film were characterized by microscopes. And various parameters which affect ZnO film properties were systematically studied: such as length, width of the thin film and the number of inkjet deposition.5) At last, we did the photosensitive test of this novel UV sensor and studied photosensitive properties of it.In conclusion, ZnO UV sensor is successfully prepared on paper substrate by direct inkjet printing technology. Moreover, these sensors are verified to be sensitive for UV with efficient and low-cost fabrication method. Thus, we propose a shadow-free method for cost-effective device fabrication.