Developments in thin film technology has led to some of the most advanced sensors currently in use across many different industries.
Thin film sensors are precise, stable, dependable and cheap, offering numerous advantages over conventional sensors. Most applications of thin film sensors take advantage of their small size and the options they provide engineers - their distinctive housing being an especially useful feature for particular applications.
Some of the more fascinating uses of the thin film sensor technology lie within the medical field. When medical pumps and irrigation systems are disrupted by a blocked tube or pump breakdown, there may be devastating and potentially deadly repercussions.
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Medical device engineers often use ‘tube sensors’ to keep track of pressure in these pump systems. These sensors work by gauging the pressure on a sensor which is placed against the widening walls of polyurethane or PVC tubing. Device makers also might place a sensor behind the pump to track pressures as the pump pushes against the sensor during operation. Thin film sensors have the shown the necessary repeatability, durability and precision needed to be effective in these and other applications.
Thin film pressure sensors are commonly used in industrial applications, particularly in hydraulic equipment and vehicles, like cranes, steamrollers, forklifts and agricultural machinery. This is because all essential functions of hydraulics require precise tracking of the hydraulic pressures.
Advantages Over Traditional Sensors
Thin film sensor devices have many advantages over conventional sensors. Thin film technology allows for a sensor element that is especially small and compact, while retaining impressive attributes in terms of precision and lasting stability. Thin films can be deposited on and fused to many kinds of substrate, including ceramic materials and high-grade specialty steels. Research has shown that the response time of these sensors is more rapid and exact, while the size allows for intimate placement and a decreased need for external circuitry.
The production methods used to produce thin-film sensors have now matured to the point that they can be made efficiently, at a low cost and with very precise specifications. There are numerous advantages to the thin film means of production. One of the many key benefits is the true molecular bond between the transducer and the deposited films. This flexure/dielectric interface is free of any organic materials and oxygen that might soak up moisture or react over time. Sputtered thin film sensors are resistant to the issues associated with organic backing materials in bonded foil gauges. The absence of organics also means these devices are capable of extreme temperature operations.
Thin film sensors are produced by directly depositing material onto fixtures in a vacuum deposition chamber by a process known as sputtering. A sputtering system allows for process control so that films may be produced with a high degree of repeatability. Considerably stricter control of bridge resistance and zero balance are typically achieved in production than are achievable with standard gauges. The film deposition rate is almost linear with input power, and the rate may be slowed adequately so that very thin films can be deposited, making use of low powers over short time periods. By adjusting sputtering parameters, gauge bridges can be created to meet challenging insulation resistance requirements.
Types of Thin Film Sensor
- High-temperature strain sensor technology – These gauges are functional in temperatures exceeding 1000 °C, which compares favorably to the 700 °C limit for conventional sensors.
- Thin film thermocouples – Useful in a range of substrate systems, thin film thermocouples can be made to be as thin as 10 μm.
- Heat flux sensors – Thermopile-type sensors measure temperature difference using thin film thermocouples, while RTD-based sensors are based on thin film RTDs.
- Flow sensors – Thin film flow sensors can measure boundary-layer flow much closer to the surface than conventional sensors; 65 μm away compared to about 250 μm.
- Multi-functional sensors – Some thin film sensors can measure temperature, pressure and heat flux all at the same time.