Quantitative imaging of dielectric permittivity and tunability
AssigneeUniversity of Maryland, College Park
InventorsSteven Mark Anlage, David E. Steinhauer, Constantine P. Vlahacos, Frederick C. Wellstood
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Abstract
A near-field scanning microwave microscope images the permittivity and dielectric tunability of bulk and thin film dielectric samples on a length scale of about 1 micron or less. The microscope is sensitive to the linear permittivity, as well as to non-linear dielectric terms, which can be measured as a function of an applied electric field. A versatile finite element model is used for the system, which allows quantitive results to e obtained. The technique is non-destructive and has broadband (0.1-50 GHz) capability.
Claims23
A method for contact imaging of dielectric permittivity using a near-field scanning microwave microscope having a resonator with a probe tip comprising the steps of:
- (a) calibrating the near-field scanning microwave microscope to determine a geometry descriptor of the probe tip, said step of calibrating the near-field scanning microwave microscope including the step of selecting a resonant frequency of the near-field scanning microwave microscope;
- (b) scanning each of at least two calibration samples, wherein for each scan the probe tip is first brought into contact with each of said at least two calibration samples;
- (c) generating calibration curves;
- (d) scanning a test sample in contact with the probe tip at scanning locations and generating at least one test sample frequency shift value at each scanning location;
- and
- (e) determining the dielectric permittivity of the test sample at the sample locations based on the respective generated test sample frequency shift values and the generated calibration curves.
An apparatus for displaying dielectric properties comprising:
- (a) a near-field scanning microwave microscope having an open-ended coaxial probe with a sharp, protruding center conductor;
- (b) a coaxial transmission line resonator that has a resonant frequency;
- (c) a microwave source coupled to said coaxial transmission line resonator through a capacitive coupler for generating said voltage;
- (d) a spring-loaded cantilever for supporting said sample in contact with said sharp protruding center conductor;
- (e) a bias tee coupled to said coaxial transmission line resonator for applying a local electric field to said sample in contact with said sharp protruding center conductor;
- (f) a first motor controller for manipulating said sample in contact with said sharp protruding center conductor in a first direction;
- (g) a second motor controller for manipulating said sample in contact with said sharp protruding center conductor in a second direction;
- (h) a third motor controller for manipulating said sample in contact with said sharp protruding center conductor in a third direction;
- (i) a coupler joined to said microwave source and said coaxial transmission line resonator;
- (j) a detector for converting the microwave signal from said coupler into an input signal;
- (k) a feedback circuit receives the output signal from said detector and measures a shift change in resonance frequency, wherein said feedback circuit keeps said microwave source locked onto a predetermined resonant frequency;
- (l) a processor for determining between at least one parameter related to a change in said resonant frequency and a known dielectric property value of a sample responsible for said change;
- wherein the processor is further able to receive from said feedback circuit said value for at least one parameter related to a change in said resonant frequency due to an unknown dielectric property of said sample and determine the value of said unknown dielectric property;
- and
- (m) a display device for imaging the value of said unknown dielectric property once said value is determined by said processor.
A method for non-contact imaging of dielectric permittivity using a near-field scanning microwave microscope having a resonator with a probe tip comprising the steps of:
- (a) calibrating the near-field scanning microwave microscope using at least three dielectric samples with known dielectric properties, said step of calibrating the near-field scanning microwave microscope further including the selection of a resonant frequency of the near-field scanning microwave microscope;
- (b) generating calibration curves;
- (c) scanning a test sample with the probe at a predetermined scanning height and generating at least one test sample frequency shift value at said predetermined scanning height;
- and
- (d) determining the dielectric permittivity of the test sample based on the generated test sample resonant frequency shift value and the generated calibration curves.
Dependencies are inferred from the claim text.