CMOS-MEMS Capacitive Humidity Sensor

Lazarus, Nathan; Bedair, Sarah S.; Lo, C.-C.; Fedder, Gary K.

doi:10.1109/jmems.2009.2036584

Cited by 71 publications

(47 citation statements)

References 17 publications

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“…the PI-2600 Series from HD Microsystems TM . Applications involve humidity sensing devices [7,[9][10][11] or pressure sensors [12][13][14], as well as a sacrificial layer for RF-MEMS switches [15][16][17]. PI can also act as a thermal insulating layer to prevent heat leakage to the substrate in nano-and microsystems thanks to a thermal conductivity of about 0.3 W m −1 K −1 [18].…”

Section: Introductionmentioning

confidence: 99%

Poling Field Dependence of Longitudinal and Transverse Wave Velocities, Young's Modulus, and Poisson's Ratio in Piezoelectric Ceramics

Ogawa¹,

Ishii²,

Matsumoto³

et al. 2012

Jpn. J. Appl. Phys.

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The interest of using polyimide as a sacrificial and anchoring layer is demonstrated for post-processing surface micromachining and for the incorporation of metallic nanowires into microsystems. In addition to properties like a high planarization factor, a good resistance to most non-oxidizing acids and bases, and CMOS compatibility, polyimide can also be used as a mold for nanostructures after ion track-etching. Moreover, specific polyimide grades, such as PI-2611 from HD Microsystems TM , involve a thermal expansion coefficient similar to silicon and low internal stress. The process developed in this study permits higher gaps compared to the state-of-the-art, limits stiction problems with the substrate and is adapted to various top-layer materials. Most metals, semiconductors or ceramics will not be affected by the oxygen plasma required for polyimide etching. Released structures with vertical gaps from one to several tens of μm have been obtained, possibly using multiple layers of polyimide. Furthermore, patterned freestanding nanowires have been synthesized with diameters from 20 to 60 nm and up to 3 μm in length. These results have been applied to the fabrication of two specific devices: a generic nanomechanical testing lab-on-chip platform and a miniaturized ionization sensor.(Some figures may appear in colour only in the online journal) Polyimide (PI) is often selected for its high planarization factor, CMOS compatibility, tolerance to most chemical products used in microfabrication, and chemical resistance up to high temperatures. Moreover, depending on its formulation, PI can be spin-coated with thicknesses as high as several tens of μm and as low as 200 nm by diluting the precursor solution in its solvant [8]. A large range of possible gaps is thus allowed between a top movable clamped-clamped membrane or beam and a fixed bottom electrode lying on the substrate. New formulations of PI show additional interesting properties such as a thermal expansion coefficient similar to silicon (Si),

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Section: Introductionmentioning

confidence: 99%

Poling Field Dependence of Longitudinal and Transverse Wave Velocities, Young's Modulus, and Poisson's Ratio in Piezoelectric Ceramics

Ogawa¹,

Ishii²,

Matsumoto³

et al. 2012

Jpn. J. Appl. Phys.

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“…That of water is about 80 [23,24], and as such causes a large change in capacitance upon absorption by a polymer. Looyenga's equation for the dielectric constant of a water-absorbing polymer is given by [24,25]:…”

Section: Sensing Principlementioning

confidence: 99%

A Simple Capacitive Sensor Array Based on a Metal-Insulator-Metal Structure

Lee¹,

Choi²,

Ahn³

et al. 2012

Journal of Sensor Science and Technology

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A simple array of metal-insulator-metal capacitive elements was proposed for a potential application in humidity sensing platforms. We fabricated meso-scale sensors with different sizes(large-size: 2.7 x 2.7 mm 2 ; mid-size: 1.5 x 1.5 mm 2 ; small-size: 0.7 x 0.7 mm 2 ) and characterized the performance of each design. Polyimide films were utilized as a humidity-sensitive layer. Capacitance changes of the polyimide layer were measured with respect to water absorption. The device showed sensitivity in the full range of relative humidity (RH) with excellent linearity(correlation coefficient > 0.994). This array structure exhibits unique advantages including easy fabrication process, high batch productivity, and high structural compatibility with various substrate materials. It is anticipated that this device structure will be potentially useful in unique applications including mapping spatial humidity variations over a meso-scale area and implementing flexible humidity sensing element arrays.

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“…The most common sensing polymers are polyimides, polymethyl methacrylate, and cellulose derivatives. 1,6,7 Polymers are generally used due to their high linearity, low cost of production, and limited hysteresis when compared with other sensing dielectrics such as porous metal oxides. However, polymer sensing materials cannot withstand high temperatures, can exhibit high hysteresis in constant high humidity environments, and tend to break down faster than their metal oxide counterparts.…”

Section: Introductionmentioning

confidence: 99%

“…5 Lazarus et al proposed an RH sensor to detect when a respirator cartridge has been nearly exhausted by utilized inkjet printing to deposit polyimide onto an integrated parallel plate electrode array built using CMOS fabrication processes. 7 Tetelin et al proposed a polyimide RH sensor based on parallel plate capacitance that achieved a 1.1 second response time for use in diagnosing pulmonary deficiencies. 8 Sen and Darabi proposed a polyimide based RH sensor that employs both interdigitated electrode and parallel plate geometries to improve sensor performance by 18% over traditional parallel plate sensors for use in HVAC applications.…”

Section: Introductionmentioning

confidence: 99%

Gelatin as a new humidity sensing material: Characterization and limitations

2014

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The goal of this work is to assert the utility of collagen and its denatured counterpart gelatin as cost-effective alternatives to existing sensing layers comprised of polymers. Rather than producing a material that will need to be discarded or recycled, collagen, as a by-product of the meat and leather industry, could be repurposed. This work examines the feasibility of using collagen as a sensing layer. Planar electrodes were patterned with lift-off process to work with the natural characteristics of gelatin by utilizing metal vapor deposition, spin coating, and photolithography. Characterization methods have also been optimized through the creation of specialized humidity chambers that isolate specific characteristics such as response time, accuracy, and hysteresis. Collagen-based sensors are found to have a sensitivity to moisture in the range of 0.065 pF/%RH. Diffusion characteristics were also analyzed with the diffusion coefficient found to be 2.5 × 10−5 cm2/s. Absorption and desorption times were found to be 20 seconds and 8 seconds, respectively. Hysteresis present in the data is attributed to temperature cross-sensitivity. Ultimately, the utility of collagen as a dielectric sensing material is, in part, due to its fibrous macrostructures as well its hydrophilic sites along the peptide chains. Gelatin was patterned between and below interdigitated copper electrodes and tested as a relative humidity sensor. This work shows that gelatin, which is inexpensive, widely available, and easy to process, can be an effective dielectric sensing polymer for capacitive-type relative humidity sensors.

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CMOS-MEMS Capacitive Humidity Sensor

Cited by 71 publications

References 17 publications

Poling Field Dependence of Longitudinal and Transverse Wave Velocities, Young's Modulus, and Poisson's Ratio in Piezoelectric Ceramics

Poling Field Dependence of Longitudinal and Transverse Wave Velocities, Young's Modulus, and Poisson's Ratio in Piezoelectric Ceramics

A Simple Capacitive Sensor Array Based on a Metal-Insulator-Metal Structure

Gelatin as a new humidity sensing material: Characterization and limitations

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