SMI Meeting New Automotive Pressure,Sensor Requirements: A Design Approach

PublishTime：2021-02-19

Automobiles are increasingly taking over functions once demanded of the driver,improving the safety, reliability and comfort of the automotive experience. Cars and trucks are constantly monitoring their environments, both externally and internally; sensors are what allow this to happen. In fact, for some types of sensor, the automotive sector represents not only the largest market, but also the fastest growing.
Pressure sensors fit into this category.Things the driver was once expected to do-monitoring the pressure in the tires,maintaining oil levels,keeping fluid levels in check-are now performed automatically,at greater frequency and accuracy than was previously possible.Some systems need to gather information so quickly that no human,or indeed any other type of sensor, is up to the task. Side airbags are an example of this, as are pedestrian-protection systems in the front bumper. For these reasons, the automotive sector now consumes 58% of the world’s pressure sensor output, and the industry is enjoying an 6% annual growth rate.
Because the market is so attractive,one could assume that all pressure sensor manufacturers serve as automotive suppliers. However,the barrier to entry for prospective automotive suppliers is high.Suppliers must be prepared to receive or maintain TS16949 as well as ISO9001 certifications, and many manufacturers require ISO14001 Environmental compliance as well. These certifications require a constant commitment to quality and continuous improvement. Additionally, suppliers to the automotive industry must be prepared for audits by the end customers for their products.So despite the attractiveness of the market, the number of options presented to the automotive system designer remains limited.
An automotive supplier must understand the key attributes the automotive industry demands: reliability, lifetime, and cost. The sensor should work 100% of the time.It should operate reliably for 10-15 years, or 150,000-250,000 miles.Finally,given the automotive industry's cost consciousness,the sensor must be economical.These demands are all the more difficult because automotive pressure sensors operate in extremely hostile environments. As engines grow smaller and hotter, the operating temperature range of the sensors continues to expand. The Automotive Engineering Council recognizes this; in 2014 Grade 4 (operating temperature from 0 ̊C to +70 ̊C)was eliminated.Currently,Grade 0 is defined as operating temperatures from –40 ̊C to +150 ̊C,but automakers are already looking beyond this to applications where +165 ̊C and higher are required.Even as the operating conditions continue to expand, performance is expected to improve, and increasing cost is not an option.
While these conditions and constraints pose formidable challenges, they are not insurmountable. Sound design protects the sensors and delivers reliability and long operational life.However, to better meet all of these requirements simultaneously, significant evolution in sensor design needs to occur.
Consider the performance limitations inherent in the sensors currently used for absolute pressure measurements in the automotive industry.Figure 1 illustrates a typical device (in this case,the SM9231 sensor from Silicon Microstructures,Inc.).This device consists of a silicon sensing wafer with glass wafers anodically bonded to the top and bottom.The top glass provides the absolute reference cavity located above the pressure-sensing membrane,which the bottom glass provides mechanical isolation between the sensing membrane and the package, as well as allowing additional bonding area on the bottom.The top glass is arranged to allow access to the bondpads on the silicon layer, while the bottom glass contains a hole to allow the pressurized f luid access to the underside of the pressure-sensing membrane.
There are tradeoffs between performance and operating temperature range for sensors of this sort.The temperature coefficient of offset and temperature hysteresis are limited by the thermal mismatch between the silicon and the top and bottom glass.To achieve both high performance as well as an extended operating temperature range,it would be preferable to avoid thermal mismatches in the region of the mechanical membrane.
The location labeled ‘A’in Figure 1 represents a stress concentra-tor at the glass/silicon interface.Under extreme pressures,or extreme rates of pressure change, the acute angle formed at this interface could become a failure site.

Brand of Product：	SMI
Part#：
Product Category：	More
Application：	More
Data Type：	White Paper More
Safety & Environment Standards：	More
Operating Temperature：	Please see the document for details
Qualification Grade：	More
Qualification Approval：	More
Package：
Language：	English Chinese Chinese and English Japanese
Date of Creation：
Version Number：
Data Encoding：
Data Size：	632 KB

Data section preview(2pages)

- The full preview is over. If you want to read the whole 6 page document,please Sign in/Register -

Download

+1 Like
Add to Favorites

Recommend

Selection Guide

More>

New Products & Solutions

More>

Technical Resources

More>

All reproduced articles on this site are for the purpose of conveying more information and clearly indicate the source. If media or individuals who do not want to be reproduced can contact us, which will be deleted.

Integrated Circuits