Simultaneous Electrothermal Test Method for Pyroelectric Microsensors

[+] Author and Article Information
Brian Smith

Mechanical Engineering Department, and Institute for Complex Engineered Systems, Carnegie Mellon University, Pittsburgh, PA 15213brs@andrew.cmu.edu

Cristina Amon

Mechanical Engineering Department, and Institute for Complex Engineered Systems, Carnegie Mellon University, Pittsburgh, PA 15213camon@cmu.edu

J. Electron. Packag 129(4), 504-511 (Aug 19, 2007) (8 pages) doi:10.1115/1.2804101 History: Received November 03, 2006; Revised August 19, 2007

Pyroelectric film materials, including polyvinylidene fluoride (PVDF) and its copolymers (e.g., P(VDF/trifluoroethylene)), are attractive candidates for low-cost infrared detection and imaging applications due to their compatibility with complementary metal-oxide semiconductor processing and inexpensive packaging requirements compared to semiconductor-based detectors. The pyroelectric coefficient (p) describes the material’s electric response to a change in sensor temperature and is the main contributor to the sensitivity and detectivity of the system. However, this value can vary greatly with film fabrication and poling processes, and its measurement is often highly coupled to the material’s thermal diffusivity. This paper describes a new approach to film characterization that combines the popular “3-omega” technique for thermal characterization with a modified version of the laser intensity modulation method for determining the film’s pyroelectric coefficient. The new method is capable of simultaneously measuring film conductivity, diffusivity, and pyroelectric coefficient. It could increase the accuracy of the pyroelectric measurements by providing in situ thermal data to the electrical model instead of relying on published values or thermal measurements of a different sample. We also present a fabrication process that can be used to pole and measure a variety of pyroelectric materials and a mathematical framework to study the thermal phenomena of the setup. The thermal model is used to highlight the methodology’s sensitivity to uncertainties in the geometric and material property values of the layers surrounding the pyroelectric film.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Typical IRFPA with integrated sensor and electronics

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Figure 2

Schematic of the 3-omega test technique

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Figure 3

Layer stackup of the proposed test setup. Labels match designations in Table 1.

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Figure 9

Agreement of 1D and 2D models when kx,n⪡kz,n

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Figure 10

Relative error between 1D and 2D models with isotropic properties: (a) full range, logarithmic scale; (b) wide bridges only, truncated range, and linear scale

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Figure 11

Sensitivity of system to input parameters

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Figure 4

3D schematic of the proposed test setup

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Figure 5

Penetration depth of thermal signal through layers

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Figure 6

Impedance contours with reference to layers in stack. The legend refers to the impedance contour lines, and the layers are labeled analogous to Fig. 5.

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Figure 7

TTF. The spatial domain is limited to the PVDF layer and is the ratio between surface impedance and the impedance at a point in the PVDF.

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Figure 8

Surface impedance using various boundary conditions

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Figure 12

Sensitivity of impedance to a chosen material property relative to the average sensitivity to the same property over all other layers and frequencies. (a) Diffusivity. (b) Conductivity.

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Figure 13

Derivative of temperature in the PVDF sample

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Figure 14

TWF in the system




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