Zheying Guo

A novel uncooled substrate-free optical-readable infrared detector: design, fabrication and performance

A novel substrate-free uncooled IR detector based on an optical-readable method is presented and fabricated successfully. The detector is composed of a bi-material (BM) cantilever array, without a silicon substrate, which is eliminated in the fabrication process. Compared with the generally used sacrificial layer cantilever, the loss of incident IR energy caused by the reflection from and absorption by the silicon substrate is eliminated completely in the substrate-free structure. The IR radiation reaching the IR detector surface increases by over 80% in the case of the novel substrate-free detector array structure, compared to the sacrificial layer structure. Moreover, the substrate-free structure has less heat loss than the sacrificial layer structure. The results of thermal imaging of the human body show the detector is able to sense objects at room temperature. The experimental NETD was estimated to be 200 mK.

Design of a Novel Substrate-Free Double-Layer-Cantilever FPA Applied for Uncooled Optical-Readable Infrared Imaging System

This paper describes the design and performances of a novel focal-plane array (FPA) containing pixels of double bimaterial-layer cantilevers without silicon (Si) substrate for being applied in the uncooled optical-readable infrared (IR) imaging system. The top layer of the cantilever pixels is made of two materials with large mismatching thermal expansion coefficients: silicon nitride (SiNx) and gold (Au), which convert IR heat into mechanical deflection. The bottom layer is SiNx cantilever, which partially serves thermal isolation legs. The top and bottom pads form the resonant cavity, which can dramatically enhance the absorption of incident IR irradiation, and the substrate-free configuration enables reducing the loss of incident IR energy. Responding to the IR source with spectral range from 8 to 14 mum, the IR imaging system may receive an IR images through visible optical readout method. A thermal-mechanical model for such cantilever microstructure is proposed, and the thermal and thermal-mechanical coupling field characteristics of the cantilever microstructure are optimized through numerical analysis method and simulation by using the finite-element method. The thermal-mechanical deflection simulated is 7.2 mum/K, generally in good agreement with what the thermal-mechanical model and numerical analysis forecast. The analysis suggests that the detection resolution of current design is 0.03 K, whereas the noise analysis from FPA indicates the current resolution to be around 100 muK and the limit noise-equivalent temperature difference (NETD) of the IR imaging system can reach to 7 mK.

Design of a Novel Uncooled Infrared Focal Plane Array

This paper presents the optimized design of a novel Focal Plane Array (FPA) structure for opt-mechanical uncooled infrared imaging system. The FPA structure is a bi-material micro-cantilever array which without Si substrate and with thermal isolation organ. In the paper, we build up series of model to describe the structures IR absorb, heat exchange and thermal-mechanical characters. To optimize the parameter for a given pixel size (200 mum times 200 mum ) and certain materials, we have studied the number of deforming cantilever and given out an optimal value. The sensitivity of the optimized structure is calculated out to be 12.2 times 10-3deg/K. which means with the optical readout system we have reported [Zheying Guo, et al.,2005], the NETD can get 1.6 mK

Circuit models applied to the design of a novel uncooled infrared focal plane array structure

This paper describes a circuit model applied to the simulation of the thermal response frequency of a novel substrate-free single-layer bi-material cantilever microstructure used as the focal plane array (FPA) in an uncooled opto-mechanical infrared imaging system. In order to obtain a high detection of the IR object, gold (Au) is coated alternately on the silicon nitride (SiNx) cantilevers of the pixels (Shi S et al Sensors and Actuators A at press), whereas the thermal response frequency decreases (Zhao Y 2002 Dissertation University of California, Berkeley). A circuit model for such a cantilever microstructure is proposed to be applied to evaluate the thermal response performance. The pixels thermal frequency (1/τth) is calculated to be 10 Hz under the optimized design parameters, which is compatible with the response of optical readout systems and human eyes.

IR Imaging at Room-temperature Using Substrate-free Micro-cantilever Array

This paper presents the structure, fabrication and imaging results of a novel optical-readable uncooled infrared detector, in which substrate-free structure is employed to replace the generally used sacrificial layer structure. This substrate-free detector with 100 times 100 pixels can eliminate the loss of 46% of the incident radiation caused by substrate reflecting. The inclination angle of the detector, when absorbing IR radiation, is measured and converted to the gray level imaged by CCD. The results of the thermal image of human body shows the detector is able to sensing the objects at room temperature. The experimental NETD was estimated to be 0.2K

Failure analysis of uncooled infrared focal plane array under a high-g inertial load

This paper describes the failure analysis of an uncooled infrared focal plane array (IRFPA) under a high-g inertial load system using finite element simulation and experimental validation methods. The uncooled IRFPA, responding to a source of infrared (IR) radiation with spectral range from 8 µ mt o 14µm, is a cantilever array, which consists of two materials with mismatched thermal expansion coefficients. The radiance distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array using a visible optical readout method. Based on this principle, room-temperature infrared imaging was developed under a static gravity environment, as described in our previous paper (Li C et al 2006 Meas. Sci. Technol. 17 1981–6). But under a dynamic inertial load, the rotation angle of every pixel includes not only the thermal–mechanical part but also a part induced by the inertial load. In the elastic deformation range, with a linearly increasing acceleration, the deformation angle induced by the inertial load increases linearly, which is validated by finite element simulation. This linear change in deformation, which can be subtracted from the total rotation angle in the optical readout using certain arithmetic, will not influence the imaging result. It is noteworthy that failure stress will occur when the deformation angle induced by the inertial load moves into the plastic deformation range, and the optical readout cannot image the IR object. Through finite element simulation the critical load resulting in IRFPA failure is 2715g, and this can be validated through impact using a Hopkinson bar after the IRFPA is placed in vacuum. By finite element simulation, the initial IRFPA surface profile without IR radiance after the 2715g load showed a conicoid characteristic. Simulation of the failure analysis of the uncooled IRFPA under 2715g acceleration predicts the military application of IRFPAs for an uncooled infrared imaging system in the high-g tactical range.