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 AlxNy thin films for using them as pyroelectric detector’s sensing material. To test the sensitivity of infrared detection or pyroelectric effect of AlxNy 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 AlxNy thin films were deposited by radio frequency (RF) sputtering from an Al target in Ar: N2 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 N2 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 × 10-9 C/m2K to 3.76 × 10-8C/m2K with a room temperature pyroelectric coefficient value of 8.60×10-9C/m2K. 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 (VOx) 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-GexSi1-xOy) 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 VOx 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.
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 (Pb1-xCaxTiO3, 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:O2 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 O2 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 × 10-12 A and 1.99 μC/m2K respectively at room temperature. The loss tangent did not change much with temperature for all the PCT samples.
This work presents the deposition and characterization of AlxNy 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 AlxNy films were deposited using an Al target and Ar:N2 = 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 AlxNy thin films were annealed at 700 0C in N2 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 × 10-14 A at 303 K to 1.75 × 10-13 at 353 K. When the temperature varied between 303 K to 353 K the pyroelectric coefficient was increased from 8.60 × 10-9 C/m2K to 3.76 × 10-8 C/m2K while the loss tangent remains almost constant to ~1.5 × 10-5 when the temperature was varied in the same range.
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 Ni0.8Cr0.2 absorber, PCT sensing layer, Ti electrodes, Al2O3 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 3.98×10-8 W/K. The second design had a longer thermal path than the first one and had a thermal conductivity of 2.41×10-8 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 4.57×10-9 W/K which is significantly lower than previously reported values. The highest calculated detectivity and reponsivity values were 1.15 × 1010 cm Hz1/2/W and 4.9 × 107 V/W respectively.
Conference Committee Involvement (1)
Image Sensing Technologies: Materials, Devices, Systems, and Applications V