Introduction and Application of Ceramic Sensors

As a cutting-edge technology of modern science and technology, sensor technology can be regarded as one of the three pillars of modern information technology. The national standard GB7665-87 defines it as: "a device or device that can sense the specified measured quantity and convert it into a usable signal according to a certain law (mathematical function law), usually composed of sensitive elements and conversion". Sensors, as a new type of special component that is being developed, are the source of detecting and obtaining external information, the most fundamental basis for the development of the Internet of Things, and the basic product in the electronic information equipment manufacturing industry. According to their manufacturing process, they can be classified into integrated sensors, thin film sensors, thick film sensors and ceramic sensors

Ceramic sensor refers to a sensing device made of ceramic material for sensing measurement signals for conversion output. Ceramic is a recognized material with high elasticity, corrosion resistance, wear resistance, impact resistance and vibration resistance. The thermal stability of ceramic and its thick film resistance can make its operating temperature range as high as -40～135℃, and it has high precision and high stability of measurement. The electrical insulation degree is >2kV, the output signal is strong, and the long-term stability is good. High-performance, low-price ceramic sensors will be the development direction of pressure sensors.

Ceramic Sensor manufacturing process

composition

In the process of making ceramic sensors, the first thing to do is to process the ceramic material:

①Screen the ceramic powder to ensure uniform particles.

②Process it into the required shape and size. The most common methods are molding, injection molding, die casting and extrusion.

③Drying and sintering. The time and temperature need to be determined according to the characteristics and shape of the ceramic material.

④Cleaning to remove impurities and dirt on the surface.

⑤Passivation treatment. Use a certain concentration of oxidizing acid or alkali to make the metal on the surface of the sensor produce an oxidation reaction with oxygen to form an oxide film.

⑥After the ceramic material is processed, the key process for making ceramic sensors is thick film screen printing, which prints the electrode layer, resistor layer and encapsulation layer respectively.

Working Principle:

The medium pressure directly acts on the ceramic diaphragm, causing the measuring diaphragm to shift. Normal pressure causes the diaphragm to shift by 0.025mm, and overpressure only causes the diaphragm to shift by 0.1mm. At this time, the measuring diaphragm is attached to the ceramic bracket to avoid damage. The capacitance generated by the diaphragm displacement is detected, amplified and converted into a standard signal output by the electronic components directly connected to it.

Ceramic Sensors classified by material properties used

Advantages of ceramic sensors

• Strong high-pressure overload capacity

The measuring range of ceramic sensors depends on the thickness of the ceramic diaphragm, so when the sensor encounters a load condition that exceeds its load, the main product will not be permanently damaged based on the base support of the diaphragm itself.

• No zero error caused by "memory" effect

Generally, metal diaphragms usually have the so-called "memory" effect (memory effect: refers to the stretching and deformation of objects whenever pressure is applied, especially high pressure, and they cannot be restored to their original state when the pressure disappears). Therefore, metal diaphragm sensors are prone to zero position errors in transmitter output.

Due to the characteristics of its structure and micro-motion, ceramic sensors can return to their original position after being subjected to pressure within a reasonable range or even exceeding the reasonable range, which improves the repeatability of transmitter output.

• Not affected by temperature

Metal diaphragm sensors are easily affected by thermal expansion and contraction, which affects their repeatability. Ceramic materials are almost not affected by thermal expansion and contraction. There is no oil filling when forming pressure gauges and absolute sensors, so there is no error caused by thermal expansion and contraction of filling liquid. This characteristic of ceramic sensors is very suitable for obtaining good repeatability measurements in occasions where temperature changes are very obvious.

Application of ceramic sensors

Ceramic sensors have been widely used in many fields due to their unique performance advantages, including automotive electronics, aerospace, environmental monitoring, medical diagnosis, etc. With the rapid development of the Internet of Things, mobile Internet, new energy and high-end equipment manufacturing industries, the growth of their market size has driven the demand for ceramic sensors. In 2023, the scale of ceramic sensors in my country will reach 21.772 billion yuan; in the automotive field, the scale will reach 5.544 billion yuan, with a compound growth rate of 16% since 2017; in other fields, the scale will reach 16.228 billion yuan, with a compound growth rate of 10.4% since 2017.

In the automotive field, ceramic sensors are mainly used in five aspects.

(i)Detecting car temperature. Negative temperature coefficient (NTC) thermistor - thermal sensors are often used to detect cooling water, intake air and engine oil temperatures. Positive temperature coefficient (PTC) thermistor - thermal sensors are often used as automobile liquid level sensors or low temperature starting heating elements.

(ii) Detecting automobile exhaust. Using solid electrolyte gas-sensitive ceramic materials, oxygen sensors for automobile exhaust monitoring are developed to measure the oxygen concentration in exhaust emissions to detect the engine air-fuel ratio. In addition to saving fuel, it can also reduce the emission of harmful gases such as CO and NO2.

(iii) Detecting the working state of the cylinder. The piezoelectric ceramic knock sensor is composed of a piezoelectric ceramic vibrator, a metal sheet, a sealing gasket, a metal shell, etc. Piezoelectric ceramics based on the piezoresistive effect can monitor the working state of the cylinder.

(iv) Guiding safe driving of the car. Ultrasonic sensors based on the piezoresistive effect are used as automobile reversing anti-collision alarm devices, also known as ultrasonic reversing radars or reversing sonar systems. Ceramic acceleration sensors can be used in automobile airbag systems.

(v) Detecting automobile humidity. Humidity sensors are suitable for detecting frost and condensation of car windows and air humidity in the intake part of the engine carburetor.

As the information source of automotive electronic control systems, automotive sensors are key components of automotive electronic control systems and one of the core contents of research in the field of automotive electronic technology. The higher the degree of automotive electronics and automation, the greater the dependence on sensors. Our company can provide you with a variety of high-quality, high-performance, and widely applicable products including ceramic sensors, and can also provide customized products upon request. Please feel free to contact us if you need any!

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