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15 Aug 2001

Volume 90, Issue 4, pp. 1683-2051

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Stability conditions, nonlinear dynamics, and thermal runaway in microbolometers

G. B. Brandão, L. A. L. de Almeida, G. S. Deep, A. M. N. Lima, and H. Neff

J. Appl. Phys. 90, 1999 (2001); http://dx.doi.org/10.1063/1.1384852 (10 pages) | Cited 3 times

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The nonlinear dynamic behavior of microbolometers, operating at room temperature (300 K) under conditions of positive electrothermal feedback is investigated. An improved device model, based on the heat balance equation is developed. It takes into account the temperature dependence of the thermophysical parameters, such as thermal coupling coefficient between the sensor and its surroundings, and sensor heat capacity and its thermal resistance coefficient. Operational considerations for thermoresistive microbolometer with positive and negative temperature coefficient of resistance are discussed for both, constant current and constant voltage modes of operation. Analytical expressions are derived for predicting stable and unstable operation. Safety factors L0, establishing the biasing conditions for stable device operation are proposed for the positive temperature coefficient of resistance and negative temperature coefficient of resistance type sensors. Limits for fast catastrophic destruction are provided, and the dynamic characteristics of the associated thermal runaway phenomenon is illustrated. This effect, as predicted by analysis and numerical simulation, was observed experimentally, confirming the validity of the proposed modeling approach for the microbolometer. © 2001 American Institute of Physics.
Show PACS
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Electron cross section set for CHF3

W. Lowell Morgan, Carl Winstead, and Vincent McKoy

J. Appl. Phys. 90, 2009 (2001); http://dx.doi.org/10.1063/1.1382833 (8 pages) | Cited 17 times

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We describe the development of a consistent set of low-energy electron collision cross sections for trifluoromethane, CHF3. First-principles calculations are used to obtain key elastic and inelastic cross sections. These are combined with literature values of the ionization cross section and with vibrational excitation cross sections obtained from the Born approximation to form a preliminary set, which is then adjusted to achieve consistency with measured swarm parameters. © 2001 American Institute of Physics.
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34.80.Gs Molecular excitation and ionization
34.80.Bm Elastic scattering
33.15.Mt Rotation, vibration, and vibration-rotation constants

Hybrid dielectric and iris-loaded periodic accelerating structure

Peng Zou, Liling Xiao, Xiang Sun, Wei Gai, and Thomas Wong

J. Appl. Phys. 90, 2017 (2001); http://dx.doi.org/10.1063/1.1383578 (7 pages) | Cited 1 time

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One disadvantage of conventional iris-loaded accelerating structures is the high ratio of the peak surface electric field to the peak axial electric field useful for accelerating a beam. Typically this ratio Es/Ea⩾2. The high surface electric field relative to the accelerating gradient may prove to be a limitation for realizing technologies for very high gradient accelerators. In this article, we present a scheme that uses a hybrid dielectric and iris-loaded periodic structure to reduce Es/Ea to near unity, while the shunt impedance per unit length r and the quality factor Q compare favorably with conventional metallic structures. The analysis based on MAFIA simulations of such structures shows that we can lower the peak surface electric field close to the accelerating gradient while maintaining high acceleration efficiency as measured by r/Q. Numerical examples of X-band hybrid accelerating structures are given. © 2001 American Institute of Physics.  
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29.20.-c Accelerators
29.27.Eg Beam handling; beam transport

Role of sp2 phase in field emission from nanostructured carbons

A. Ilie, A. C. Ferrari, T. Yagi, S. E. Rodil, J. Robertson, E. Barborini, and P. Milani

J. Appl. Phys. 90, 2024 (2001); http://dx.doi.org/10.1063/1.1381001 (9 pages) | Cited 32 times

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It is shown that sp2 phase organization plays an important role in the field emission from nanostructured carbons. Emission is found to depend on the cluster size, anisotropy, and mesoscale bonding of the sp2 phase, and the electronic disorder. It is found by Raman spectroscopy that increasing the size of sp2 clusters in the 1–10 nm range improves emission. Anisotropy in the sp2 phase orientation can help or inhibit the emission. sp2 clusters embedded in the sp3 matrix or electronic disorder induced by localized defects oriented in the field direction can provide a local field enhancement to facilitate the emission. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.U- Carbon/carbon-based materials
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
81.07.Bc Nanocrystalline materials
78.30.Na Fullerenes and related materials
71.55.Ht Other nonmetals
71.55.Jv Disordered structures; amorphous and glassy solids
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