Advantages of Thin Film Technology in Sensors & Transducers

There are certain applications where pressure sensors are deployed in very harsh environments. For instance, aircraft systems are very complex and are required to work under inhospitable environmental conditions. Temperature alone can vary from being extremely low to unusually high depending on where the transducer is being used on the aircraft. Due to these extreme conditions, the sensors or transducers used in aerospace applications should ideally be able to withstand harsh operating conditions.

This is where thin-film technology comes in. Transducers with thin-film technology are more rugged, lightweight, and simple than other sensors on the market while also being cheaper and more reliable. Let’s see why and how.

mems sensor diagram

Figure 1: Typical MEMS Sensing Element

Types of Pressure Transducer Technologies

First, let us start off with a bit of background information on pressure transducers. The term transducer is used to describe any device that converts variations in a physical quantity to proportional electrical signals. Pressure transducers typically use piezoresistive strain gage technology, usually in a Wheatstone bridge, that senses pressure changes and converts them into an electrical output. Strain gauge technologies used in aircraft pressure transducers are broadly classified into two types: Micro-Electro-Mechanical Systems (MEMS) and Thin Film. The most commonly used technology being MEMS (Figure 1 illustrates a typical MEMS-based pressure sensor).

How MEMS systems work

In MEMS sensor technology, the pressure of the media is measured by a silicon or silicon-on-insulator sensing element that has the piezoresistive strain gage bridge on it, with a transfer medium, typically silicon oil, present between the MEMS element and a stainless-steel diaphragm. The pressure exerted on the diaphragm is transferred to the MEMS element through the oil. The change in pressure results in a change in electrical output from MEMS elements piezoresistive strain gage. This electrical output gives us an indication of the pressure changes within the system.

Where does MEMS technology fall short?

MEMS Sensor Diaphragms before and after extreme temperature testing

Figure 2: MEMS Sensor Diaphragms before and after extreme temperature testing

MEMS pressure sensors do have some drawbacks. First, MEMS devices are very complex and their design and manufacturing process is quite complicated. This complexity is one of the reasons for the high costs of these devices.

Second, the accuracy and reliability of MEMS transducers largely depends on the complex fabrication and design of the insulated diaphragm. On top of all that, the silicone oil within the device can undergo thermal expansion or shrinkage when used in very high or very low temperatures. Figure 2 shows what happens when a MEMS sensor is tested at temperatures below -40oF. This is a major issue as thermal expansion and shrinkage can damage the stainless-steel diaphragm which requires replacement of the transducer.

The Better Choice: Thin Film Sensors and Transducers

thin film sensor depiction

Figure 3: Thin Film Sensor

Thin film sensors are more robust and less complex than MEMS sensors. Their simple structure makes them easier to manufacture at a lower cost and they provide incredible accuracy and reliability even in harsh operating conditions such as extreme temperatures (less than -40oF and as high as 392oF). 

In thin film sensor technology, a piezoresistive strain gauge bridge is deposited directly on the cell’s stainless-steel diaphragm which is in direct contact with the media being measured. See Figure 3.  With this technology, there is no transfer medium in between the media and sensing bridge measuring the pressure. This eliminates the damaging expansion or shrinkage that can occur in the MEMS device.

In a nutshell, thin film transducers work where other transducers fail. They can easily withstand dynamic pressures and extreme temperatures while providing the most accurate and reliable readings. Thin film sensors are especially suitable for harsh operational conditions such as pressure measurements in aerospace applications. If you’re searching for a transducer that can do it all in a lightweight, durable package, look no further than Custom Control Sensors’ Gen 3 thin film pressure transducers.

For over 60 years, CCS has been a leader in the design, testing, manufacturing, and supply of standard and custom pressure, temperature, and flow switches and transducers for the Aerospace, Defense, Industrial, and Energy markets. Our products continue to push the limits of what is possible with these devices, allowing us to facilitate the advancement of the industries we supply. For more information on transducers with thin film technology, check out our products for the aerospace industry or call us directly.

 

2020-03-26T23:42:12+00:00March 26th, 2020|Uncategorized|

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