Low Temperature Synthesis and Electro-Mechanical Testing of Zinc Oxide Thin Films on Polymeric Substrates
Conventionally, Zinc Oxide (ZnO) requires high sintering temperatures (~1100?C). We aim to make use of ZnO nanoparticles and achieve low temperature (less than 240?C) sintering for use with polymeric substrates. The thin film fabricated will be inspected for atomic
2025-06-28 16:28:31 - Adil Khan
Low Temperature Synthesis and Electro-Mechanical Testing of Zinc Oxide Thin Films on Polymeric Substrates
Project Area of Specialization Mechanical EngineeringProject SummaryConventionally, Zinc Oxide (ZnO) requires high sintering temperatures (~1100°C). We aim to make use of ZnO nanoparticles and achieve low temperature (less than 240°C) sintering for use with polymeric substrates. The thin film fabricated will be inspected for atomic and electromechanical qualities. Polymeric sintering of ZnO is an attractive advancement in various micro-electronic, medical and sensing technologies.
This experimental work aims to add to the ever-expanding applications of thin films. ZnO has many conventional uses in the medicinal and the photovoltaic industries due to its insolubility in water, relatively low toxicity, and biodegradability in general and more specifically, its piezoelectric properties. Research studies in the field of microelectromechanical systems (MEMS) have led toward the development of many innovative and advanced devices and the potential advances for non-medicinal applications even surpass that of the current medicinal uses. ZnO nanorod sensors, spintronics, and piezoelectricity are all very promising fields.
A report published by Grand View Research in 2016 claims that MEMS have great potential of becoming a multibillion-dollar industry by 2024. It is notable that the key which has led towards the possibility of such futuristic devices is the involvement of stretchable and flexible substrates in combination with thin films based on nanostructured materials.
All these advantages however, come at a cost, one which is not very attainable in third world countries. Given the prerequisites, our objective is to document a methodology that can sustainably and affordably output ZnO thin films sintered on polymers at low temperatures.
Project ObjectivesWe aim to put forward a simple, easy, cost-effective, energy-efficient, and most importantly, a scalable thin-film synthesis regime. The deciding factor that determines the success of our methodology relies upon the results obtained for SEM and XRD (sintering confirmation) and also the mechanical testing results. For a successful test, our goal is that the thin film material must undergo minimal changes in its morphology and electromechanical properties with respect to the stretch and flex experienced by the substrate-thin-film matrix. The fabrication technology for stretchable electronics requires vacuum-based techniques, such as physical vapor deposition, chemical vapor deposition, and such novel and expensive technologies. They require many auxiliaries and time-consuming steps. They require high process temperatures, which can produce adverse effects on film morphology due to the phenomenon of residual thermal stresses. In view of the hurdles above, alternate fabrication technologies such as spin coating, blade coating, rod coating, and ink-jet printing with solution-based direct writable inks, can be considered as possible options.
In concise terms, our objectives are:
- To sinter Zinc Oxide nanoparticles on polymer substrate at a low temperature.
- To achieve low temperature sintering of ZnO nanoparticals on polymer substrate.
- To develop thin films of ZnO nano-particles on flexible polymer substrate.
- To develop a process which is energy efficient and can be used on a large scale.
- To develop an economical and sustainable method of sintering.
- To study nano structure of films formed using SEM.
- To study electromechanical properties of ZnO thin films on polymer substrate .
- To study piezoelectric properties of ZnO thin films.
Our polymer of choice is room-temperature-vulcanizing (RTV) silicone. It matches the scope of our project for its low curing temperature, relative ease of molding, and price. A few simple laboratory procedures and chemicals can make RTV more hydrophilic (attracted to water) and thus resulting in overall better adhesion to the sintered ZnO nanoparticles. A preliminary ink solution is made comprising of a particular amount of ZnO nanoparticles mixed in a solvent with a low boiling temperature. Our solvents of interest are Ethanol and Ethylene Glycol. The ink is coated onto the cured RTV sample and left in a drying oven at a certain temperature for a certain period of time. Both temperature and time are varied to study the resultant sintering, or lack thereof.
Electromechanical testing preliminarily validates the design and provides diagnostics of the fabricated material. Qualitative tests can be carried manually by group members and validated by the project supervisor while quantitative testing can be carried out on the universal testing machine available at the Mechanical Department Engineering laboratories.
The results of our fabrication require intricate imagery and analysis of the sintered nanoparticles to confirm the composition of the thin film. X-ray diffraction (XRD) is the first step of micro analysis that confirms the crystal phases present and validates the presence of ZnO in the fabricated thin film. Scanning Electron Microscopy (SEM) shows surface topography, material interaction, and micro fractures. SEM helps us see at a micro level to evaluate the quality of the fabricated thin film. These tests need to be outsourced due to unavailability at the Mechanical Engineering Department laboratories.
Benefits of the ProjectThe world is progressing towards Nano technology. Our project core is nano films and nano technology. Znic Oxide has vast application in nano science and nano technology.
- Zinc Oxide is bio-compatible, low toxic, semi-conductor and piezoelectric.
- ZnO nanoparticles are used in many industrial products such as paint, rubber, coating, and cosmetics. They are used in biological applications due to their excellent biocompatibility, economic, and low toxicity. ZnO is currently listed as a “generally recognized as safe (GRAS)” material by the Food and Drug Administration and also used as food additive.
- Zinc Oxide is a biocompatible material hence, it is compatible with living tissue. Biocompatible materials do not produce a toxic or immunological response when exposed to the body or bodily fluids.
- Zinc Oxide is also piezoelectric in nature, it is able to generate an electric charge in response to applied mechanical stress. It’s a semiconductor material, having an electrical conductivity value falling between that of a conductor and an insulator. Zinc Oxide is also Water Insoluble and can be applicable in MEMS setups where chances of exposure to moisture are high.
- Zinc oxide owing to its relatively high conductivity, electron mobility, stability against photocorrosion and availability at low-cost, is an attractive material for solar cell applications, especially Thin Film Solar Panels. In solar panels, doping of Zinc Oxide at P-N junction causes formation of N junction. Zinc Oxide helps in achieving greater efficiencies from solar panels. Hence, can also be used in energy harvesting.
- Due to vast application of zinc oxide and zinc oxide nano films, our project can be very beneficial to the field of MEMS and Nano technology. And development of a method which is economical, energy effeicient and less time consuming can be a revolutionary to this field.
Due to limited time and monetary constraints, conventional machining was carried out on university premises using a milling machine to obtain a single 1 mm deep cavity that is 50 mm long and 8 mm wide on a thin Aluminum block. The resulting cavity was filled with Grey RTV Silicone and the excess removed by a sharp razor for a flush even finish with the cavity dimensions as shown below. The resulting filled cavity was left for 24 hours under room temperature conditions to cure, completely dry, and form the desired substrate and then carefully extracted.
This procedure is done to modify surfaces to have a strong attraction to water. This is the opposite of hydrophobic treatments which make surfaces repel water. Some materials are naturally hydrophobic, meaning water beads up into droplets and it does not spread out evenly onto the surface. Few basic ways are:
• Surface energization
• Grit blasting
• Ozone treatment
We used Polyvinylpyrrolidone (PVP) and Sodium hydroxide (NaOH) as surface treating chemicals.
Fabrication of ZnO Ink:Experimental work began with Ethanol as the solvent for the ZnO ink. However, as it will be discussed in our results, a switch to an Ethylene Glycol based ZnO ink was explored. Both the ink preparations followed the schematic procedure pictured below where a calculated amount of the solvent was weighed and the desired calculated percent by weight amount of ZnO nanoparticles were added and mixed to form a solution. The container is the placed in a ultrasonic bath for 30 to 40 minutes to allow even better macro and micro mixing and better dispersion of ZnO nanoparticles throughout the solvent.
The films were fabricated using a non-vacuum, scalable, and cost-effective method of rod coating. A lab micropipette was used on its lowest setting to pick a small volume of ink droplets. These 2-3 drops were deposited on one edge of the substrate and a stainless-steel rod was slowly moved back and forth to ensure an even dispersion of the ink onto the substrate. Any visible discontinuity of the film was rectified by adding a few additional drops and repeating the rod movement again. It is important to note that the substrate was placed on an oiled double layered glass slide. The oil allows ease of removal of the substrate-thin-film matrix while the double layering helps stop the bottom of the substrate from burning.
The product was placed in a baking oven and was heated to 225 °C and was kept at that temperature for 90 minutes. After baking, the product was kept inside the baking oven in order to cool down to room temperature for 24 hours.
| Item Name | Type | No. of Units | Per Unit Cost (in Rs) | Total (in Rs) |
|---|---|---|---|---|
| Total in (Rs) | 36102 | |||
| Zinc Oxide nanoparticles | Equipment | 1 | 21000 | 21000 |
| Silicone RTV | Equipment | 4 | 250 | 1000 |
| Silver Conductive Paste | Equipment | 1 | 850 | 850 |
| Glass Slide | Equipment | 72 | 4 | 252 |
| Beaker | Equipment | 4 | 250 | 1000 |
| Petri Dish | Equipment | 2 | 200 | 400 |
| SEM Imaging | Miscellaneous | 4 | 2500 | 10000 |
| Distilled Water | Equipment | 1 | 800 | 800 |
| Tape (Double sided, Kapton) | Equipment | 2 | 200 | 400 |
| Sandpaper | Equipment | 2 | 100 | 200 |
| Paper Cutter | Equipment | 1 | 200 | 200 |