TERAHERTZ SENSOR BASED ON DIELECTRIC METASURFACE

Abstract

A terahertz sensor based on a dielectric metasurface, including a sensing element, and a thermosensitive circuit connected to the sensing element. The sensing element is composed of a cylindrical semiconductor doped with a conductive material. The conductive material is configured to change conductivity of the cylindrical semiconductor to enable the cylindrical semiconductor to absorb electromagnetic waves in terahertz region.

Claims

1. A terahertz sensor based on a dielectric metasurface, comprising: a sensing element; and a thermosensitive circuit connected to the sensing element; wherein the sensing element is composed of a cylindrical semiconductor doped with a conductive material; the conductive material is configured to change electrical conductivity of the cylindrical semiconductor to enable the cylindrical semiconductor to absorb electromagnetic waves in terahertz region; the terahertz sensor is micron-sized; the conductive material is boron; and the cylindrical semiconductor has a radius of 95-110 μm and a height of 85-95 μm; and the cylindrical semiconductor doped with the conductive material is prepared through steps of: (S1) pretreating a cylindrical silicon nitride substrate; (S2) subjecting a boron target to magnetron co-sputtering in argon to deposit a boron-doped silicon nitride film on the cylindrical silicon nitride substrate, wherein during the magnetron co-sputtering, the cylindrical silicon nitride substrate is subject to a bias voltage; and (S3) subjecting the cylindrical silicon nitride substrate to photo-thermal annealing under nitrogen gas for 1-2 h; and (S4) cooling the cylindrical silicon nitride substrate to obtain a boron-doped cylindrical semiconductor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 schematically illustrates a simulation model of a terahertz sensor according to an embodiment of the present disclosure;

[0029] FIG. 2 is a resonance curve of the simulation model of the terahertz sensor according to an embodiment of the present disclosure;

[0030] FIG. 3a is a Y-direction electric field plot of the simulation model of the terahertz sensor according to an embodiment of the present disclosure;

[0031] FIG. 3b is an X-direction electric field plot of the simulation model of the terahertz sensor according to an embodiment of the present disclosure;

[0032] FIG. 4a shows change of thermal conductivity (k) of Si.sub.3N.sub.4 with temperature;

[0033] FIG. 4b shows change of constant pressure heat capacity (Cp) of Si.sub.3N.sub.4 with temperature; and

[0034] FIG. 5 shows surface temperature of the terahertz sensor according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0035] The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by one of ordinary skill in the art based on the embodiments of the present disclosure without paying any creative efforts shall fall within the scope of the present disclosure.

[0036] The terahertz sensor in this application achieves the required wave absorption performance based on single resonance unit, that is, the terahertz sensor only includes one wave-absorbing resonance unit. As shown in FIG. 1, the resonance unit is Si.sub.3N.sub.4, in which a conductive material is doped to impart a certain conductivity to the Si.sub.3N.sub.4. After being directly and vertically incident on the surface of the resonance unit, the electromagnetic waves will be absorbed to generate electromagnetic heat in the form of dielectric loss and conduction loss. Then the generated electromagnetic heat will affect the impedance of the thermistor attached below (not illustrated in FIG. 1), leading to the impedance change in the circuit of the thermistor. The circuit plays a role as a temperature control sensor in some mechanical automatic operations.

[0037] Inspired by the above working principle, this application provides a terahertz sensor based on a dielectric metasurface, which includes a sensing element, and a thermosensitive circuit connected to the sensing element. The sensing element is composed of a cylindrical semiconductor doped with a conductive material. The conductive material is configured to change conductivity of the cylindrical semiconductor to enable the cylindrical semiconductor to absorb electromagnetic waves in terahertz region.

[0038] Preferably, the terahertz sensor is micron-sized.

[0039] Preferably, the conductive material is boron.

[0040] Preferably, the cylindrical semiconductor is a silicon nitride cylinder.

[0041] Preferably, the silicon nitride cylinder has a radius of 95-110 um and a height of 85-95 um.

[0042] Preferably, the cylindrical semiconductor doped with the conductive material is prepared through the following steps.

(S1) Pre-Treatment

[0043] A cylindrical silicon nitride substrate is pretreated.

(S2) Sputtering

[0044] A boron target is subjected to magnetron co-sputtering in argon to deposit a boron-doped silicon nitride film on the cylindrical silicon nitride substrate, where during the magnetron co-sputtering, the cylindrical silicon nitride substrate is subject to a bias voltage.

(S3) Annealing

[0045] The cylindrical silicon nitride substrate is subjected to photo-thermal annealing under nitrogen gas for 1-2 h.

(S4) Cooling

[0046] The cylindrical silicon nitride substrate is cooled slowly to obtain a boron-doped cylindrical semiconductor.

[0047] In the actual manufacturing and operation processes, the wave band required by the product can be found by modifying the size, shape and conductivity of the sensor to test the absorption rate.

[0048] After the absorption resonance curve of the required wave band is plotted, the heat generated under the frequency corresponding to the highest absorption rate is tested.

[0049] The conductivity and size of the sensor are modified to reach the maximum absorption rate.

[0050] The conductivity of the silicon nitride film can be easily measured by using the thermoelectric performance measuring device such that a film with desired conductivity can be prepared.

[0051] When the radius and height of the silicon nitride cylinder is 105 μm and 92 μm, respectively, the obtained simulation diagram is shown in FIGS. 3a-b. Referring to the simulation results shown in FIG. 2, the absorption rate of the model reaches 98% or more at 0.71 THz. Furthermore, as shown in FIG. 5, the simulation analysis shows the temperature distribution of the wave absorbing structure at a frequency of 0.71 THz and a port input power of 0.1 mW, where the highest temperature is up to 317.77 K.

[0052] As shown in FIGS. 4a-b, the silicon nitride is heated by electromagnetic heat. The temperature increase will change some properties of the material. FIGS. 4a-b show characteristic change curves of the silicon nitride over temperature.

[0053] Boron is a poor conductor at room temperature and a good conductor at an elevated temperature. By doping a proper amount of boron in the silicon nitride cylinder, the conductivity of the silicon nitride can reach about 25 S/m.

[0054] The embodiments of this application demonstrate the absorptivity of the terahertz sensor and the temperature distribution under specific frequency and incident power. Though the infrared imaging detection is not illustrated herein, the specific operation should be understood by one of ordinary skill in the art.

[0055] Described above are merely illustrative of the disclosure, which are not intended to limit the disclosure. It should be understood that various changes, modifications, substitutions and variations made by one of ordinary skill in the art without departing from the principles and spirit of the present disclosure shall fall within the scope of the present disclosure defined by the appended claims.