Abstract
This article proposes a meliorated multi-frequency band pyroelectric sensor for detecting subjects with various velocities, namely extending the sensing frequency under good performance from electrical signals. A tactic, gradually increasing thickness of the ZnO layers, is used for redeeming drawbacks of a thicker pyroelectric layer with a tardy response at a high-frequency band and a thinner pyroelectric layer with low voltage responsivity at a low-frequency band. The proposed sensor is built on a silicon substrate with a thermal isolation layer of a silicon nitride film, consisting of four pyroelectric layers with various thicknesses deposited by a sputtering or aerosol deposition (AD) method and top and bottom electrodes. The thinnest ZnO layer is deposited by sputtering, with a low thermal capacity and a rapid response shoulders a high-frequency sensing task, while the thicker ZnO layers are deposited by AD with a large thermal capacity and a tardy response shoulders a low-frequency sensing task. The fabricated device is effective in the range of 1 KHz~10 KHz with a rapid response and high voltage responsivity, while the ZnO layers with thicknesses of about 0.8 μm, 6 μm, 10 μm and 16 μm are used for fabricating the meliorated multi-frequency band pyroelectric sensor. The proposed sensor is successfully designed, analyzed, and fabricated in the present study, and can indeed extend the sensing range of the multi-frequency band.
Highlights
Pyroelectric sensors function by making use of the pyroelectric effect
A general pyroelectric sensor consists of a pyroelectric layer sandwiched between top and bottom electrodes, which is built on thermal-isolation structures or substrates for minimizing heat loss
When a heat source with a constant temperature variation rate is applied on a pyroelectric device, the temperature variation rate in the pyroelectric device should be altered by changing the thickness of the pyroelectric film, the structure of the pyroelectric film and the material of the pyroelectric film
Summary
Pyroelectricity can be described as the generation of surface charges during the change of spontaneous polarization with temperature. A variable temperature in pyroelectric materials causes the generation of free charges on the surface, perpendicular to the direction of polarization. A general pyroelectric sensor consists of a pyroelectric layer sandwiched between top and bottom electrodes, which is built on thermal-isolation structures or substrates for minimizing heat loss. When a heat source with a constant temperature variation rate is applied on a pyroelectric device, the temperature variation rate in the pyroelectric device should be altered by changing the thickness of the pyroelectric film (thermal capacities), the structure of the pyroelectric film (trenches or cavities) and the material of the pyroelectric film (the absorption coefficient of radiation and the pyroelectric coefficient). The voltage responsivity (Rv) can be expressed as [4]:
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