We report the deposition and characterization of 𝐴𝑙<sub>𝑥</sub>𝑁<sub>𝑦</sub> thin films to use them as pyroelectric detector. 𝐴𝑙<sub>𝑥</sub>𝑁<sub>𝑦</sub> thin films were deposited using a direct current (DC) magnetron sputtering from an Al target with varying concentrations of Ar:N2 at constant pressure and substrate temperature. The film thickness' were varied between 100-200 nm with varying atomic composition based on Ar:N<sub>2</sub> during deposition. The nitrogen content in the films varied from 39.0% to 44.7% as found by energy dispersive spectroscopy (EDS). Each of the thin films was annealed at a different temperature between 400 to 800 °C with 100 °C increment in N<sub>2</sub> environment and X-ray diffraction (XRD) was performed to analyze the annealed films crystallinity. From the XRD data and by using Scherrer equation, we found that for samples annealed at 600 °C for fifteen minutes has the grain size of 12.28 nm. Optical properties of the films were measured with varying wavelengths which include transmission, reflection, absorption, refraction coefficient, extinction coefficient and the optical bandgap. We also determined the electrical properties of thin films’ which include the pyroelectric coefficient, pyroelectric current, dielectric constant, and film permittivity between the temperature range 270 K to 310 K. As the temperature is increased, the pyroelectric coefficient also increased almost linearly. The pyroelectric coefficient of annealed 𝐴𝑙<sub>𝑥</sub>𝑁<sub>𝑦</sub> films found to be varied between 4.86 × 10<sup>-5</sup> C/m<sup>2</sup>K to 1.32 × 10<sup>-4</sup> C/m<sup>2</sup>K. The optical transmittance through the as grown non-annealed thin films was found to be varied between 35 to 78%, while the reflectance was found to be below 25%. Because of low absorption in the thin films the extinction coefficient was found to be near zero. The refractive index was varied between 1.7 and 2.2 for the 𝐴𝑙<sub>𝑥</sub>𝑁<sub>𝑦</sub> thin films. The optical bandgap was found to be 1.40 eV for non-annealed 𝐴𝑙<sub>𝑥</sub>𝑁<sub>𝑦</sub> thin film which was deposited on cover glass. The dielectric constant was varied between 30-1200000 depending on the annealing temperature of the film, while the film permittivity ranges between 0-1.25×10<sup>-5</sup> F/m.
Pyroelectric materials show a change in their spontaneous polarization due to the temperature variations. This property makes these materials unique for sensing radiation in the infrared (IR) broad range. Here, we report the deposition and characterization of pyroelectric Calcium Lead Titanate (PCT) thin films for using them to fabricate pyroelectric detectors. PCT films were deposited on both silicon and Si/SiN/Ti/Au substrates at 13 mTorr pressure by 200W Radio Frequency (RF) sputtering in Ar+O<sub>2</sub> environment for four hours. Substrates were kept at variable temperatures starting from 550 ºC up to 800 ºC during the deposition. The PCT films were annealed at 550, 600, 650 and 700 ºC in O<sub>2</sub> environment for 15 minutes. X-ray diffraction (XRD) results confirm the polycrystalline nature of these films. Energy dispersive spectroscopy (EDS) function of scanning electron microscope (SEM) was done to determine the elemental composition of PCT films. Our EDS result reveals the presence of the elements such as Calcium, Lead, Titanium , and Oxygen in the thin films. Moreover, it shows that the films are stoichiometric (Ca0.43Pb0.57)TiO3 (Ca/Ti=0.5, Pb/Ti=0.66). The film thicknesses were measured using a Dektak model XT profilometer which ranges from ~ 250 to 400 nm. The surface morphology obtained from SEM and atomic force microscopy confirms the crack-free nature of our films as well as their smoothness and low surface roughness. Temperature dependence of capacitance, pyroelectric current, and pyroelectric coeeficient were investigated for different PCT films. Our results show that films deposited at 550ºC and 600 ºC demonstrate better quality and larger values of pyroelectric coefficient. On the other hand, the capacitance fabricated on the PCT films at 550 ºC showed the highest value of pyroelectric current and pyroelectric coefficient which are 14 pA and 50 μC/m2K respectively at higher temperature.
Two dimensional (2D) materials have become a growing subject in the last 15 years mainly due to the isolation of graphene, which created a completely different class of material based on its unique, monolayer design. Since then, various stable materials of few atoms thick are showing emerging capabilities in optical electronics and photonics. Semiconducting monolayers of transition metal dichalcogenides (TMDs) such as MoS<sub>2</sub>, Mo<sub>1-x</sub>WxS<sub>2</sub>, and WS<sub>2</sub> exhibit direct electronic band gaps; bulk crystals display indirect band gaps. Interestingly, these 2D materials show significant light interaction over a broad bandwidth ranging from infrared to ultraviolet wavelengths. The materials allow photodetection in this bandwidth without the need of cooling, thus creating new potential for uncooled detection. In this review, we discuss various 2D materials and their interaction with light for photodetection applications.
Uncooled infrared detectors are utilized in various radiometric devices and cameras because of their low cost, light weight and performance. A pyroelectric detector is a class of uncooled infrared detector whose polarization changes with change in temperature. Infrared radiation from objects falls on top of the sensing layer of the pyroelectric detector and the absorbed radiation causes the temperature of the sensing layer to change. This work describes the deposition and characterization of Al<sub>x</sub>N<sub>y</sub> thin films for using them as pyroelectric detector’s sensing material. To test the sensitivity of infrared detection or pyroelectric effect of Al<sub>x</sub>N<sub>y</sub> thin films, capacitors of various sizes were fabricated. The diameter of the electrodes for capacitor used during testing of the device was 1100 μm while the distances between these two electrodes was 1100 μm. On a 3-inch diameter cleaned silicon wafer, 100 nm thick Al<sub>x</sub>N<sub>y</sub> thin films were deposited by radio frequency (RF) sputtering from an Al target in Ar: N<sub>2</sub> environment. On top of this, a 100-nm thick Au layer was deposited and lifted off by using conventional photo lithography to form the electrodes of capacitors. All the layers were deposited by RF sputtering at room temperature. The thin film samples were annealed at 700 °C in N<sub>2</sub> environment for 10 minutes. X-ray diffraction showed the films are poly-crystalline with peaks in (100), (002) and (101) directions. When the temperature varied between 303 K to 353 K, the pyroelectric coefficient was increased from 8.60 × 10<sup>-9</sup> C/m<sup>2</sup>K to 3.76 × 10<sup>-8</sup>C/m<sup>2</sup>K with a room temperature pyroelectric coefficient value of 8.60×10<sup>-9</sup>C/m<sup>2</sup>K. The non-annealed films were found to be transparent between the wavelengths of 600 nm to 3000 nm. The refraction coefficient was found to be varied between 2.0 and 2.2 while the extinction coefficient was found to be zero. The optical bandgap determined using Tauc’s equation was 1.65 eV.
Microbolometer arrays are the most used technology in thermal infrared imaging. Recent progress in materials and fabrication techniques for these devices have sparked much competition. Vanadium oxide (VO<sub>x</sub>) has been and is currently the most used material for commercial use of bolometers, followed by amorphous silicon (a-Si). However, other silicon derivatives, such as silicon-germanium (a-SiGe, poly-SiGe, and a-Ge<sub>x</sub>Si<sub>1-x</sub>O<sub>y</sub>) have shown promise in the recent years. Extensive research is performed to search for different bolometer materials that combine performance, lowcost, and convenience for uncooled thermal infrared imaging applications. In this review article, we discuss materials derived from VO<sub>x</sub> and Si and their fabrication process used in microbolometers, as well as important figures of merit such as temperature coefficient of resistance, responsivity, detectivity and resistivity.
This work presents the deposition and characterization of Al<sub>x</sub>N<sub>y</sub> thin films for using them as pyroelectric detector material. To test the pyroelectric effect, capacitors with Au electrodes were fabricated. The diameter of the electrodes for capacitor used was 1100 μm while the distances between these two electrodes was 2200 μm. On a 3- inch diameter cleaned silicon wafer a 100-nm thick Al<sub>x</sub>N<sub>y</sub> films were deposited using an Al target and Ar:N<sub>2</sub> = 1:1 flow and 5 mTorr chamber pressure. Finally, a 100-nm thick Au layer was deposited and lifted off by using conventional photo lithography to form the electrodes of capacitors. All the layers were deposited by radio frequency sputtering at room temperature. The Al<sub>x</sub>N<sub>y</sub> thin films were annealed at 700 <sup>0</sup>C in N<sub>2</sub> environment for 10 minutes. X-ray diffraction showed that the films are poly-crystalline with peaks in (100), (002) and (101) directions. The pyroelectric current increased from 3.38 × 10<sup>-14 </sup>A at 303 K to 1.75 × 10<sup>-13</sup> at 353 K. When the temperature varied between 303 K to 353 K the pyroelectric coefficient was increased from 8.60 × 10<sup>-9</sup> C/m<sup>2</sup>K to 3.76 × 10<sup>-8</sup> C/m<sup>2</sup>K while the loss tangent remains almost constant to ~1.5 × 10<sup>-5</sup> when the temperature was varied in the same range.
Pyroelectric detectors are the class of thermal detectors which change their spontaneous polarization when there is a change in temperature. The change in the spontaneous polarization occurs due to the absorption of infrared radiation which eventually produces a voltage. This work demonstrates the deposition and characterization of calcium modified lead titatante (Pb<sub>1-x</sub>Ca<sub>x</sub>TiO<sub>3</sub>, PCT) thin films for using them as materials of pyroelectric thermal detectors. The PCT thin films were sputtered using an RF sputter system in Ar:O<sub>2</sub> environment at room temperature. The thin films were grown on Au electrode. The capacitance was formed by using Au electrodes on top of PCT thin films which were fabricated by sputtering and liftoff. The PCT films were annealed at 450, 500, 550 and 600 °C in O<sub>2</sub> environment for 15 minutes. Energy dispersive spectroscopy was done to determine the atomic composition of PCT films. Variations of capacitance, pyroelectric voltage, loss tangent and pyroelectric current between the temperature range 303 K to 353 K were determined. The PCT films were annealed at 550 °C showed the highest value of pyroelectric current and pyroelectric coefficient of 2.45 × 10<sup>-12</sup> A and 1.99 μC/m<sup>2</sup>K respectively at room temperature. The loss tangent did not change much with temperature for all the PCT samples.
Pyroelectric detector is a class of thermal detector in which the change in temperature causes the change in the spontaneous polarization in the sensing material. In this work, we report the design of uncooled pyroelectric detectors which utilized a nanometer sized truss to support the suspended detector. The design and performance of pyroelectric detectors have been conducted by simulating the structure with Intellisuite™ utilizing Finite Element Method (FEM). The simulated detectors had a spider web-like structure with each of the strut of spider web had a width of 100 nm. Ca modified lead titanate (PCT) was employed as the thermometer because of its high pyroelectric figure of merit. The pyroelectric detectors utilized Ni<sub>0.8</sub>Cr<sub>0.2</sub> absorber, PCT sensing layer, Ti electrodes, Al<sub>2</sub>O<sub>3</sub> structural layer to obtain low thermal conductance between the detector and Si substrate. Three different types of pyroelectric detectors were designed and analyzed. The first design had linear electrode and simple spider web support. The value of the thermal conductance of this detector was found to be 3.98×10<sup>-8</sup> W/K. The second design had a longer thermal path than the first one and had a thermal conductivity of 2.41×10<sup>-8</sup> W/K. The design was optimized for the best result by modifying the shape, dimension and thickness of various layers namely absorber, electrodes, sensing layer and struts. The thermal conductance of the third design was found to be as low as 4.57×10<sup>-9</sup> W/K which is significantly lower than previously reported values. The highest calculated detectivity and reponsivity values were 1.15 × 10<sup>10</sup> cm Hz<sup>1/2</sup>/W and 4.9 × 10<sup>7</sup> V/W respectively.
RF sputtered thin films of Si<sub>1-x</sub>Ge<sub>x</sub> and Si<sub>1-x</sub>Ge<sub>x</sub>O<sub>y</sub> were investigated by measuring their composition, electrical, and optical properties. As Si concentration was increased to the Ge to form Si<sub>1-x</sub>Ge<sub>x</sub> films, the resistivity was increased while the activation energy and TCR both were decreased. For Si<sub>1-x</sub>Ge<sub>x</sub>O<sub>y</sub> films, the addition of O<sub>2</sub> to the Si<sub>1-x</sub>Ge<sub>x</sub>, increased the resistivity, activation energy and TCR. The TCR was measured to vary from -2.27%/K to -8.69%/K, while the resistivity varied from 4.22×10<sup>2</sup> Ω-cm to 3.47×10<sup>9</sup> Ω-cm. A good atomic composition of Si1-xGexOy to be used in microbolometers as the sensitive layer was found to have a TCR of -5.10%/K with a moderate resistivity of ~10<sup>4</sup> Ω-cm. Microbolometers using doped Si<sub>0.15</sub>Ge<sub>0.85</sub> and Si<sub>0.15</sub>Ge<sub>0.85</sub>O<sub>y</sub> thermometers have been fabricated using a polyimide sacrificial layer. The 1/f-noise is observed to be relatively high in the Si<sub>1-x</sub>Ge<sub>x</sub> thin films and microbolometers.