Sensor Components

MEMSIC, Inc. designs, manufactures and markets CMOS Micro-Electro-Mechanical Systems (MEMS) IC products that have on-chip mixed signal processing. MEMSIC is the first and the only company that integrates a MEMS inertial sensor with mixed signal processing circuitry onto a single chip using a standard CMOS IC process. This combination of technology has successfully yielded products at substantially lower cost and higher system performance and functionality than competitive products in the market for sophisticated accelerometers. In addition, this technological approach allows the Company to easily integrate additional functions, or create new sensors, using the standard CMOS IC process to expand into other MEMS application areas beyond accelerometers. The unique single silicon chip design approach fundamentally reduces cost and enhances the chip's performance, functionality and quality beyond what is possible with other technologies.

Thermal Accelerometer

Accelerometers were traditionally based on capacitive or piezoresistive technology that measures the movement of a micro-mechanical mass structure. Such technology possesses inherent issues such as surface adhesion, known as stiction, hysteresis, mechanical ringing, electromagnetic interference (EMI), expensive custom fabrication process, and other challenges associated with micro-mechanical moving structures. In order to resolve these issues, MEMSIC has developed a disruptively different technology that addresses the challenges typically associated with traditional MEMS based accelerometers. Based on a patented unique thermal technology, MEMSIC is the world's first company to offer thermally based MEMS inertial sensor with mixed signal processing circuitry on a single chip using standard CMOS process.

MEMSIC’s unique thermal technology uses heated gas molecules to detect acceleration and is the fundamental principle behind our accelerometer IC products. They work in any orientation and are available in either a XY of XZ package configuration providing you with the design flexibility you need to meet your customers’ most demanding requirements. The ASIC and sensing elements are integrated onto a single piece of silicon. The simplicity of a single die approach translates into low cost and industry leading ppm and reliability without sacrificing performance. 

The unique single silicon chip design approach fundamentally reduces cost and enhances the chip's performance, functionality and quality beyond what is possible with other technologies. The principal of operation of MEMSIC devices is based on heat transfer by natural convection.

The devices measure internal changes in heat transfer caused by acceleration, offering significant advantages over the use of a traditional solid proof-mass structure. Since the proof mass in the MEMSIC sensor design is gas molecules, movable mechanical structures are eliminated within the accelerometer. The result is the ability for a MEMSIC accelerometer to withstand a theoretical shock limit over 50,000g, which is over 5X that of traditional accelerometers, and also to eliminate the problems associated with the surface adhesion known as stiction.

In addition, special handling and testing that add significant OEM costs are no longer required. MEMSIC's standard CMOS compatible process along with its high quality manufacturing capability allows MEMSIC to consistently produce the highest quality accelerometers with failure rates up to several thousand times better than that of traditional MEMS based accelerometers. Such technology and manufacturing ability fundamentally eliminates the unacceptable failure rates and production costs associated with other accelerometer technologies, and positions MEMSIC as the perfect solution for consumer applications, where high shock environments are common and high failure rates are not accepted. This mix of high quality and value opens up a world of new features for consumer products not previously possible with traditional MEMS accelerometers.

Temperature sensors equidistant from the heater measure the same temperature until device is accelerated as shown in top picture. Acceleration of the sensor creates a non-symmetrical temperature profile from which acceleration is detected as shown in the lower picture.

Anisotropic Magnetor-Resistive (AMR) Technology

MEMSIC magnetometers are based on anisotropic magnetoresistive (AMR) technology. Magnetoresistance is the property of a material to change the value of its electrical resistance when an external magnetic field is applied to it. Anisotropic Magnetoresistance (AMR) is the property of a material in which a dependence of electrical resistance on the angle between the direction of electrical current and orientation of magnetic field is observed. The effect is attributed to a larger probability of s-d scattering of electrons in the direction of magnetic field. The net effect is that the electrical resistance has maximum value when the direction of current is parallel to the applied magnetic field.

The AMR sensors are special resistors that vary with the magnetic field. MEMSIC magnetometers use AMR Permalloy film as magnetic field inducting components. During manufacturing a strong magnetic field is applied to the film to orient its magnetic domains in the same direction, establishing a magnetization vector. When an external magnetic field is applied to the film, the magnetization vector angle changes relative to the current flowing through the permalloy film, which in turn changes the film’s resistance. The resistance variation is directly proportional to the angle between the magnetization vector and the current vector.

To compensate for the non-linear characteristics and inability to detect the polarity of a magnetic field, a somewhat more complex structure is used for sensors. It consists of stripes of aluminum or gold placed on a thin film of permalloy (a ferromagnetic material exhibiting the AMR effect) inclined at an angle of 45°. This structure forces the current not to flow along the "easy axes" of thin film, but at an angle of 45°. The dependence of resistance now has a permanent offset which is linear around the null point.

The AMR effect is used in a wide array of sensors for measurement of Earth's magnetic field (electronic compass), for GPS navigation and for magnetic field detection applications.