Microsensors and smart sensors are emerging technologies that have rapidly developed in recent years. The technical terms currently used in Chinese newspapers and magazines are still rather ambiguous, often referring to them as sensors or vaguely lumping them together as automotive semiconductor devices. Some also lump smart sensors (or smart actuators, smart transmitters) together with microsystems and MEMS under the term MEMS (microelectromechanical systems). Here are the definitions and technical connotations of some commonly used technical terms in current European and American publications.
First of all, it must be pointed out that in most cases, the sensors mentioned in the titles and full text of this article actually refer to three major categories of devices: sensors that convert non-electrical input parameters into electromagnetic signal outputs; actuators that convert electrical signals into non-electrical parameter outputs; and transmitters that can be used as both sensors and actuators, among which the most common are those that convert one form of electromagnetic parameter into another form of electromagnetic parameter output.
The technical characteristics of microsensors and smart sensors can be extended to microactuators and microtransmitters—sensors (or actuators, or transducers) with at least one physical dimension equal to or less than the submillimeter scale. Microsensors are not simply a physical reduction of traditional sensors, but rather a new generation of devices based on semiconductor process technology. They utilize novel operating mechanisms and physicochemical effects, employ materials compatible with standard semiconductor processes, and are fabricated using microfabrication techniques. Therefore, they are sometimes also called silicon sensors. Similar definitions and technical characteristics can be used to describe microactuators and microtransmitters.
It consists of two chips: an accelerometer unit (microaccelerometer) with self-test capabilities, and the interface circuitry between the microsensor and a microprocessor (MCU). This device, a relatively early one (circa 1996), is already quite practical, used in automotive automatic braking and suspension systems. Because the microaccelerometer has self-test capabilities, it can also be used in airbags. This example clearly demonstrates that the advantage of microsensors lies not only in their reduced size but also in their ease of integration with integrated circuits and mass production. This two-chip solution can shorten the design cycle and reduce the cost of small-batch trial production in the early stages of development. However, for actual applications and the market, a single-chip solution is clearly more desirable, with lower production costs and higher application value.
Smart sensors, smart actuators, and smart transmitters are devices that integrate a microsensor (or microactuator, or microtransmitter) and some or all of its processing components and circuitry on a single chip (for example, the single-chip solution for the microaccelerometer mentioned above). Therefore, smart sensors possess certain biomimetic capabilities, such as fuzzy logic operations, active environmental identification, automatic adjustment and compensation to adapt to the environment, self-diagnosis, and self-maintenance.
Obviously, to achieve scale and reduce production costs, the design philosophy, material selection, and production process of smart sensors must be as consistent as possible with standard planar silicon integrated circuit processes. Specialized steps can be added to the normal process flow before, during, or after wafer fabrication, but these steps should be minimal.
The device integrates a micromechanical pressure sensor with an analog user interface, an 8-bit analog-to-digital converter (SAR), a microprocessor (Motorola 69HC08), memory, and a serial interface (SPI) on a single chip. The silicon pressure sensor at the front end is fabricated using bulk silicon micromachining technology.
