Design and optimization of an ultra thin flexible capacitive humidity sensor (original) (raw)
Related papers
Humidity sensor integrated with polysilicon TFT based read-out interface on flexible substrate
In this work we show the design and fabrication process of a read-out interface based on polysilicon TFTs technology integrated with capacitive humidity sensor. All the devices were fabricated on a thin flexible polyimide substrate (8 µ m) according to a low temperature polysilicon (LTPS) fabrication process (<350°C). We proposed as read-out interface a three stages ring oscillator circuit, employed to convert the sensor capacitance variation into output frequency change. The sensor capacitor is a three layer interdigitated capacitor (IDC). The transducers layout has been optimized by means of 3D Finite Element simulations in order to increase the response speed, considering the diffusion of the water molecules into the chemical interactive material (CIM). In particular we have compared two different sensor structures, one with the upper metal shaped in fingers 20 µ m wide (IDC1) and an alternative structure (IDC2) with the upper metal divided in squares 15 µ m wide. We have chos...
Sensors and Actuators B: Chemical, 2011
In this paper we present the design and fabrication of a fully flexible sensorial system, composed of three different sensor units implemented on an ultrathin polyimide substrate of 8 m thick. Each unit is composed by a capacitive chemical sensor integrated with readout electronics. The sensors are parallel plate capacitors with the top electrode properly patterned to allow analytes diffusion into the dielectric that acts as chemical interactive material. Three different polymers, poly(tetrafluoroethene) (PTFE), poly(methyl 2-methylpropenoate) (PMMA) and benzocyclobutene (BCB), were used as dielectrics. A ring oscillator circuit, implemented with polysilicon thin film transistors (PS-nTFT), was used to convert the capacitance variations into frequency shifts. The electronic tests show oscillating frequencies of about 211 ± 2 kHz and negligible frequency shifts under different bending radius conditions. Furthermore, system response to some alcohols concentrations (Methanol, ethanol, 1-butanol, and 1-propanol) is reported and data analysis proves that the system is able to discriminate methanol from ethanol.
A Capacitive Humidity Sensor Suitable for CMOS Integration
IEEE Sensors Journal, 2000
This paper describes the design, fabrication, and performance of a thin film humidity sensor fabricated in standard CMOS process, hence it may be combined with an integrated circuit. The sensor is based on a capacitance between interdigitated electrodes in the top metal layer and water adsorption in the polyimide layer. The design is optimized by analytical and then finite element models which show that, within the constraint of the CMOS structure, the sensitivity can be no greater than one third of the sensitivity of the polyimide alone. Experimental sensors were fabricated in-house before an improved design was fabricated in a commercial foundry. The different behavior of these sensors, despite their similar designs, leads to an investigation into the effects of fabrication process on the sensor linearity. Characterizing the polyimide film by contact angle, AFM and FTIR revealed that the difference in linearity of the response between the two sensors resulted from different etching techniques employed to pattern the film.
Capacitive Humidity Sensor Based on Polymer Composite Thin Film
2018
Nowadays humidity sensors are used in every industry, such as in food, pharmaceuticals [1], medicine, [2] and agriculture [3, 4]. These commercial humidity sensors are quite expensive, complicated in operation, and have low sensitivity and stability because of the materials used as a sensing element [5]. It is difficult to maintain their operational cost, power losses, sensitivity and stability [4]. Therefore, it is essential for a sensor to have high sensitivity and stability, low cost, small hysteresis, wide linear range, simple operation, short response, and short recovery time [5, 6]. Electrical conduction is affected significantly by dipoles of water molecules, which makes it important for researchers to investigate the magnitude of change in impedance and capacitance of the samples with respect to varying relative humidity. The investigation becomes more important for composite materials due to the contribution of properties by two or more ingredients. Changing the constitutin...
A polyimide based resistive humidity sensor
Sensor Review, 2005
PurposeTo establish an accurate and sensitive method to characterize the moisture content of a particular environment.Design/methodology/approachThis paper proposes a relatively simple humidity sensor design consisting of electrodes on a suitable substrate coated with a polyimide material. The changes in relative humidity are denoted by a corresponding change in the polyimide material's electrical resistance profile. The design proposed in this work can be microfabricated and integrated with electronic circuitry. This sensor can be fabricated on alumina or silicon substrates. The electrode material can be made up of nickel, gold or aluminum and the thickness of the electrodes ranges typically between 0.2 and 0.3 μm. The sensor consists of an active sensing layer on top of a set of electrodes. The design of the electrodes can be configured for both resistive and capacitive sensing.FindingsThe polyimide material's ohmic resistance changes significantly with humidity variations...
Integrated Temperature, Humidity and Gas Sensors on Flexible Substrates for Low-Power Applications
2007 IEEE Sensors, 2007
Temperature, gas and humidity resistive/ capacitive sensors on flexible substrates from organic materials, suitable for RFID mobile applications, have been produced and investigated. The sensor implementation solutions are providing simple, versatile and low power temperature and gas detection. The device structure was developed together with the data evaluation strategies based on last generation Σ∆ analog (resistance and capacitance) to digital converters. We demonstrate the possibility of developing gas sensors on humidity sensitive substrates, having temperature corrected responses. The proposed device concept is aimed to evolve towards "flexible & full plastic" implementations.
DESIGN OF HIGH SENSITIVITY AND FAST RESPONSE MEMS CAPACITIVE HUMIDITY SENSOR
TJPRC, 2013
This paper presents a model which predicts the temporal response of capacitive humidity sensors made of parallel electrodes and a polymer sensitive coating. This model is used for the simulation of the response of the sensor subjected to specific conditions. The model includes electrostatic and molecular diffusion calculation. As an application example, the model is used to simulate the response of several humidity sensor structures exposed to the conditions of a medical application related to breath analysis. The model may also be helpful to predict the effects of fabrication process uncertainties. Because the model used to describe water diffusion in Polyimide is based on Henry’s law and Fick’s law, it could be extended to the optimization of capacitive sensors for other vapours
Humidity Microsensor with Polyimide Sensitive Layer
fett.tu-sofia.bg
A new humidity microsensor has been developed and fabricated by a microelectromechanical system (MEMS) technology and thin-film technology, using Polyimide thin film. The way of sensing is in connection with the adsorption of the humidity ...
Fully printed organic thin film transistors (OTFT) based flexible humidity sensors
2013 IEEE SENSORS, 2013
A flexible fully printed organic thin film transistor (OTFT) was successfully fabricated and employed as a humidity sensor. The bottom gated OTFT, with width to length ratio (w/l) ratio of 26, was printed on a flexible poly ethylene terephthalate (PET) substrate. Conductive gate and dielectric layers were printed using gravure printing technique. Source and drain electrodes were deposited by means of screen printing. An active layer of pentacene, a humidity sensitive material, was deposited using inkjet printing. The current-voltage characteristics of the fully printed device were studied from 25% RH to 90% RH. A percentage change of 2000 % at 90% RH, in the drain current (I D ), was registered when compared to the I D at 25% RH. The response of the fully printed sensor towards relative humidity was studied and is reported in this paper.
Capacitive sensors realized on flexible substrates
2017
The article presents design and realization results of capacitive sensors realized on flexible substrates. Presented planar capacitive sensors were realized by standard polymer and ink-jet printing technologies at two different polymer substrates. Developed flexible planar capacitive sensors can be used as a standard mechanical keyboard replacement by journalists (touch-typists) where low response time is required, or e.g. in medical environment, where high level of hygiene is required. Fully configurable design and high level of flexibility predestine these capacitive sensors to be used in almost every application to replace mechanical switch wear out by almost unlimited lifetime.