The sensor revolution over the past few years has resulted in a shift to the mass production and use of sensors in almost every imaginable application. The integration of semiconductors into these sensors has been largely supported by the increasing number in our smartphones.
What Are Semiconductors?
Semiconductors are materials that are neither good conductors nor good insulators. In semiconductors (like silicon, silicon carbide, and gallium arsenide), free charge carriers can be produced by supplying the device with energy.
Semiconductor materials are usually created using a process known as doping, which involves introducing a controlled amount of impurities into a material to control its electrical properties. By using doping techniques, positively or negatively charged semiconductors can be produced with elements that have a lesser and greater number of electrons, respectively, as compared to the original semiconductor material.
The application of semiconductor devices can be found in almost every technology used today, ranging from cars, phones, computers and much more. For example, integrated circuits (ICs) based on semiconductors alone make up over $200 billion dollars of the semiconductor industry.
With a growing number of semiconductor applications arising in the fields of molecular electronics, microelectromechanical (MEMS) devices, area-selective deposition, chemical sensors, and biological sensors; it is safe to say that semiconductors play a dominant role in modern technology.
Desirable Semiconductor Properties for Sensors
When semiconductors are incorporated into solid-state sensors, the fundamental properties, such as energy band structure, must be considered to ensure that the type of material is best suited for that particular sensor.
For example, piezoresistive sensors are primarily composed of silicon because this material can act as the sensor’s carrier and can have complex band edge structures. Other important property considerations for sensor applications include direct energy gaps and compatibility with integrated circuitry.
Semiconductors in Gas Sensors
As compared to other sensing technologies, metal oxide semiconductor gas sensors offer several advantages including greater robustness, longer lifespans, relatively low cost, high material sensitivity and fast response times.
According to the band theory, metal oxide semiconductor films used as gas sensors function by allowing the target gas to interact with the surface of the film directly. This interaction results in a change in the charge carrier concentration of the material, which ultimately changes the conductivity, or resistivity, of the metal oxide film.
Some of the most commonly used metal oxide semiconductor gas sensors include those that monitor carbon monoxide (CO) and nitrogen dioxide (NO2), as well as ammonia (NH3) and carbon dioxide (CO2) levels for environmental monitoring purposes.
Semiconductors in Smartphone Sensors
There are more than ten different types of sensors that can be found in the average modern smartphone, which include touch, acceleration, magnetic reading, and proximity sensors.
Samsung, for example, has created a novel complementary metal oxide semiconductor (CMOS) image sensor that can create vibrant and exceptionally clear images, regardless of the external environment. Backed by their ISOCELL Bright Tetracell technology, Samsung smartphone cameras automatically improve the light sensitivity of during imaging, especially when present in low-light conditions.
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- “Image Sensor” – Samsung
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