piezoelectric sensor part 3 - uni-frankfurt.de

LECETURE 6

Piezoelectric sensor

Part 3

Prof. Dr. YU GU

GU@chemie.uni-Frankfurt.de

Office Room: N160/517

One of the practicalapplications of quartzoscillators is sensingto detect mass.

This type of measurement isQCM, which measure themass from the resonantfrequency of the quartzoscillator, which depends onthe mass adsorbed onsurface of the quartz.

The QCM is a simple,cost effective, high-resolution mass sensingtechnique, based uponthe piezoelectric effect.

an applied

mechanical

force

the internal

generation

of electrical

charge

the internal

generation of

a mechanical

strain

an applied

electrical

field

Direct

piezoelectric

effect

Reverse

piezoelectric

effect

The high sensitivity andthe real-time monitoring ofmass changes on thesensor crystal make QCM avery attractive techniquefor a large range ofapplications.

QCM technique hasrecognized as a standardtool that able to provideboth qualitative andquantitative informationabout their target materials.

Photograph of typical quartz crystal resonators as usedfor QCM, metallized with gold electrodes (left: frontelectrode, right: back electrode) by vapor deposition.

The core of the QCMtechnique is the piezoelectricAT-cut quartz crystalsandwiched between a pairof electrodes.

Quartz crystal structure

Silicon dioxide

chemical formula: SiO2

Melting point: 1750 C

Density: 2.65g/cm3

Shear modulus, hardness…

Z axis, Optical axis

X axis, Electric axis

Y axis, Mechanical axis

Distribution of crystal axis of

natural quartz crystal

1. Quartz crystal

2. Electrode material

ΔF= - 2 F02ΔM/A（q q）

1/2

ΔF: Frequency Change of Quartz Crystal;

ΔM: Mass Change of the Substance on Electrode

Gold film electrodes as thesubstrate for adsorption studies.

The resonance frequency of thecrystal was determined by usingthe crystal as the frequency-determining element of anelectronic oscillator.

The QCM is an ultrasensitiveweighing device, consisting of athin disk of single crystal quartz,with metal electrodes depositedon each side of the disk. Thecrystal can be made to oscillate atits resonant frequency, whenconnected to an external drivingoscillator circuit.

A great deal of attentionwas paid to the depositionof a thin layer on varioussurfaces.

Mechanism for In-situ adsorption routes of target into QCM surface

Mechanism for indirect adsorption routes of target into QCM surface

Indirect Route for Adsorption Process

Indirect Route for Adsorption Process

In-situ and indirect routes for QCM surface for the adsorption

process of various materials.

QCM are classifiedaccording to the way thewafer is cut relative to thenatural crystallographicorientation of quartz.

Polished grade, 5 MHz（ 8 MHz ，10 MHz…）, AT cut quartz crystal was employed for this study.

QCM sensor’s surfacecan be functionalizedwith organic andinorganic materials toimprove its sensitive andselective efficiency.

Thin films with desired propertiesand functionalities have beensynthesized by various availablemethods.

chemical oxidation, electrochemical synthesis,

spin-coating, dip-coating, drop-coating,

thermal evaporation, Langmuir–Blodgett

and self-assembly techniques

Homework （Materials for the Seminar course）

• Please describe a kind of preparation method and application of functionalized film for QCM.

• You need to report them in the seminar course.

THANK YOU!