Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times

Steele, J.J.; Fitzpatrick, Glen; Brett, Michael

doi:10.1109/jsen.2007.897363

Cited by 70 publications

(30 citation statements)

References 7 publications

(8 reference statements)

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“…Capacitance humidity sensors consisting of OAD TiO 2 nanostructures deposited on interdigitated electrodes were developed some time ago by Brett et al [202,[464][465][466]. Although other OAD materials respond to humidity variations (e.g., SiO 2 and Al 2 O 3 ), sensors utilizing TiO 2 exhibit the greatest change and show an exponential increase from $1 nF to $1 lF when the humidity changes from 2% to 92% [467].…”

Section: Gas and Vapor Sensorsmentioning

confidence: 99%

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Barranco

Borrás

González‐Elipe

et al. 2016

Progress in Materials Science

599

436

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a b s t r a c tThe oblique angle configuration has emerged as an invaluable tool for the deposition of nanostructured thin films. This review develops an up to date description of its principles, including the atomistic mechanisms governing film growth and nanostructuration possibilities, as well as a comprehensive description of the applications benefiting from its incorporation in actual devices. In contrast with other reviews on the subject, the electron beam assisted evaporation technique is analyzed along with other methods operating at oblique angles, including, among others, magnetron sputtering and pulsed laser or ion beam-assisted deposition techniques. To account for the existing differences between deposition in vacuum or in the presence of a plasma, mechanistic simulations are critically revised, discussing well-established paradigms such as the tangent or cosine rules, and proposing new models that explain the growth of tilted porous nanostructures. In the second part, we present an extensive description of applications wherein oblique-angle-deposited thin films are of relevance. From there, we proceed by considering the requirements of a large number of functional devices in which these films are currently being utilized (e.g., solar cells, Li batteries, electrochromic glasses, biomaterials, sensors, etc.), and subsequently describe how and why these nanostructured materials meet with these needs.

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Section: Gas and Vapor Sensorsmentioning

confidence: 99%

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Barranco

Borrás

González‐Elipe

et al. 2016

Progress in Materials Science

599

436

View full text Add to dashboard Cite

show abstract

“…17,18,25,[31][32][33] For example, it was reported that a highly organized Al 2 O 3 -based nanomaterial, deposited by glancing angle deposition (GLAD, which is a modified PVD deposition technique offering the possibility to control morphology on a 10 nm scale), is able to detect humidity change on a millisecond time scale, which is one of the fastest humidity sensor responses reported to date. 33 Single SnO 2 nanowires were obtained by a CVD technique and revealed high sensitivity to relative humidity. 25 The main disadvantages of sensors utilizing such materials for high volume applications are the need for extensive additional development to achieve reproducible process techniques suitable for implementation in a manufacturing environment and the increased cost of the sensors that would result from the use of expensive equipment in production (CVD, PVD, etc).…”

Section: ' Introductionmentioning

confidence: 99%

TiO₂/LiCl-Based Nanostructured Thin Film for Humidity Sensor Applications

Buvailo

Xing

Hines

et al. 2011

ACS Appl. Mater. Interfaces

109

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A simple and straightforward method of depositing nanostructured thin films, based on LiCl-doped TiO 2 , on glass and LiNbO 3 sensor substrates is demonstrated. A spin-coating technique is employed to transfer a polymer-assisted precursor solution onto substrate surfaces, followed by annealing at 520°C to remove organic components and drive nanostructure formation. The sensor material obtained consists of coin-shaped nanoparticles several hundred nanometers in diameter and less than 50 nm thick. The average thickness of the film was estimated by atomic force microscopy (AFM) to be 140 nm. Humidity sensing properties of the nanostructured material and sensor response times were studied using conductometric and surface acoustic wave (SAW) sensor techniques, revealing reversible signals with good reproducibility and fast response times of about 0.75 s. The applicability of this nanostructured film for construction of rapid humidity sensors was demonstrated. Compared with known complex and expensive methods of synthesizing sophisticated nanostructures for sensor applications, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), this work presents a relatively simple and inexpensive technique to produce SAW humidity sensor devices with competitive performance characteristics.

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“…It has been previously shown that nanostructured thin films produced by glancing angle deposition (GLAD) [5]- [8] exhibit a measurable and repeatable response to variations in RH, while using optical and capacitive methods to observe these changes. Shifts in capacitance of three orders of magnitude have been observed for a change of RH from 2% to 92% [9]. In addition, extremely fast response times are observed, typically 90-300 ms [9]- [11].…”

Section: Introductionmentioning

confidence: 98%

“…Shifts in capacitance of three orders of magnitude have been observed for a change of RH from 2% to 92% [9]. In addition, extremely fast response times are observed, typically 90-300 ms [9]- [11].…”

Section: Introductionmentioning

confidence: 98%

Reactive Ion Etching of Columnar Nanostructured ${\rm TiO}_{2}$ Thin Films for Modified Relative Humidity Sensor Response Time

et al. 2009

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A CF 4 dry etch recipe for TiO 2 was optimized for nanostructured thin films. The impact of our etching process and ultraviolet irradiation of nanostructured relative humidity (RH) sensors was studied. Reactive ion etching of titanium dioxide decreased device adsorption response time by opening high diffusivity channels while retaining the high surface area and high dynamic range of the interdigitated electrode device. The full electrical response (impedance and phase) and response time of our sensors was studied as a function of etch duration. Using a TiO 2 etch recipe consisting of CF 4 produced large changes to RH sensor electrical response and introduced a large hysteresis. As a result of significant microstructural change, the adsorption response time of the RH sensors is greatly improved from 150 ms to an instrument-limited 50 ms. The adsorption times are at least six times faster than previous, thinner sensors. However, the current sensors do not recover as well as previous sensors, possibly due to nodular defects observed here and which are absent in previous devices. Although sensor step desorption times improved from an unetched 130 ms to the instrument limit of 50 ms, full recovery times increased beyond 3 s. When the etch treatment was followed by a 48 h ultraviolet treatment, the hysteresis introduced by the CF 4 etch was significantly reduced, without reducing the improvement in response time.

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Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times

Cited by 70 publications

References 7 publications

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

TiO₂/LiCl-Based Nanostructured Thin Film for Humidity Sensor Applications

Reactive Ion Etching of Columnar Nanostructured ${\rm TiO}_{2}$ Thin Films for Modified Relative Humidity Sensor Response Time

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Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times

Cited by 70 publications

References 7 publications

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

TiO2/LiCl-Based Nanostructured Thin Film for Humidity Sensor Applications

Reactive Ion Etching of Columnar Nanostructured ${\rm TiO}_{2}$ Thin Films for Modified Relative Humidity Sensor Response Time

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TiO₂/LiCl-Based Nanostructured Thin Film for Humidity Sensor Applications