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Pressure Sensors And State-Of-The-Field

HYUNG JOON

Pressure is one of important quantities in the environment like temperature, humidity etc even the human can’t sense it directly in our normal life domain. However, the pressure sensor has good and enough sensitivity to measure the few Pascal of pressure changing (i.e 1Pa = 8cm altitude change) even if you can’t feel the difference of pressure when you move up or down and sensing of pressure sensor can be used to provide significant information for our life in various applications and the usage of pressure sensing is becoming more diverse in different application domains from Automotive to Consumer markets.

According to latest market analysis report, global pressure sensor market is being growth CAGR of  7.3% over the forecast period 2018 to 2023 and it’s expected to 6.7B USD in Y2023 from 4.4B USD in Y2019 and its market is being driven by mainly automotive segment with high pressure range sensor but consumer market segment shows the fastest growth market for pressure sensor from Y2013 when pressure sensor started to be used in mobile phone and portable application and there are more new applications are coming with pressure sensor to user and the market will be more growth and diverse application is coming to us with pressure sensor.

Figure 1 in below shows ST pressure sensor evolution since 1st barometric pressure sensor was announced on 2011. The ST has announced the new pressure sensor almost every year adopting new features or enhancement what customers request and ST has enhanced the performance and improved robustness to diverse environmental condition with unique ST own technology of sensor and package solution and it contributes ST to take leadership in the consumer & mobile phone markets.

ST Pressure
Figure 1. ST Pressure sensor evolution.

STMicroelectronics has plan to prepare more wide portfolio of pressure sensors and broaden market segment to Industrial and automotive application with high volume manufacturing capability, reliable quality and high performance what ST built up in consumer market.

Sensing technology on Pressure Sensor

Mainly resistive & capacitive different sensing technology are being used on pressure sensors and each technology has own pros and cons because of different own characteristic of resistive and capacitance. ST has full capability of both technologies (i.e ST is market leader of inertial MEMS Sensor which is capacitive technology) and ST had applied the resistive technology for pressure sensor considering good linearity & sensitivity of piezo resistive technology and capability of compensation of weak TCO (temperature coefficient offset) by ST dedicated temperature compensation method and high-tech technology embedded in the sensors and the Package technology would be also one of key important factor to decide the performance as it will be explained in next paragraph.

Pressure Sensor

Sensing element of pressure sensor was designed with piezo-resistors of Wheatstone bridge on membrane as like Figure 3 and it’s mechanically designed to change the resistance according to pressure applied to membrane. This technology can give good linearity and sensitivity to measure the pressure values at wide range of pressure but resistor itself has variation by temperature so it causes bad TCO and it needs to be compensated by temperature sensor. All of ST pressure sensors embeds the temperature sensor near to sensing element to compensate TCO variation caused by temperature using dedicated algorithm embedded in sensor and it’s one of differentiated feature then competitors who normally need compensation algorithm working outside of sensor like Application process or MCU etc.

Piezo Resistor
Figure 3. Piezo-resistor on Wheatstone bridge of ST pressure sensor

Robustness to environment in manufacturing and market.

Package robustness is one of important factor to be considered in the application because air flow need to be secured for pressure measurement in the sensor device but it can cause inferior robustness to diverse environmental condition.

Most of pressure sensors are designed with cavity package solution which has empty space inside of IC to secure the air flow for pressure measurement. However, this package structure could be

weakness to environment of final application manufacturing or real-user condition because the sensor can be contaminated or damaged through holes on package during manufacturing and it can be reliability failures under harsh user condition.

ST was aware of this package weakness through ST predecessors produced on Y2013 and ST has developed innovative package solution to minimize the air flowing on full-molding package to be superior robustness to end customer manufacturing process and harsh user condition.

Package Structure
Figure 4. Package structure of ST pressure sensor vs general cavity PKG

It’s one of state of art package for pressure sensor in ST to be differentiated with other pressure sensor competitors and this solution was proven in the market with several hundred Mpcs shipment from Y2014 for diverse applications.

Wide portfolio pressure sensors in ST

Pressure sensor market is one of growing market with more diverse applications which request different performance specification and robustness to harsh condition. ST has mainly two different group of pressure sensors, barometric pressure sensor and Water-resistant pressure sensor which can cover different market and different specific performance application.

The LPS22HH as barometric pressure sensor is so accurate and stable that manufactures can eliminate one-point calibration (OPC) after soldering to increase throughput and efficiency. With a pressure noise equivalent to 5cm, the LPS22HH enhances controls such as collision avoidance & altimeter control for Drone or other unmanned vehicles. Its superior accuracy also enhances features of smartphones and sport watches and indoor navigation for vertical position etc.

STMicrotechnology

With tiny form factor on full-molding package, the LPS22HH also enhances robustness of reliability to control the features of air flow monitoring application which can be exposed to harsh condition like vacuum cleaner, air conditioner and FAN controllers.

For further information: Click here

The LPS33HW as water-resistant pressure sensor is designed to be durable up to 10Bar Water pressure with unique cylindrical metal package and the electric components inside of IC can be also protected by potting GEL to water or other harsh chemicals.

With superior robustness package & pressure noise equivalent to 6.5cm, the LPS33HW can enhance the feature of vertical position on wearable watch application which can be used for swimming or diving and water depth monitoring inside of water tank, washing machine and agriculture IoT application.

Superior robustness PKG of LPS33HW can contribute to extend the coverage of design on diverse application such as e-cigarette application which can use pressure sensor to detect and monitor puff of smoking without risky of sensor damage and defect by e-juice (nicotine)

MEMS Pressure Sensor

For further information: Click here

Some applications where pressure sensor could be useful are

  • GPS application such as tracking and Telematics
  • Wearable for rock climbing to detect height
  • Appliances such as Fan, Air conditioners, Air purifier to monitor Air flow
  • Vaccum Cleaner to detect if the dust bag is full
  • Indoor navigation to detect the floor
  • Enhanced Pedometer to monitor the altitude during a workout
  • Weather monitoring station
  • E-Cigarette to detect the puff.
  • Washing machine to detect and control the water depth

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BiS Team

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