The Vibration Actuation of Microcantilever Sensors and Their Applications on Materials Science
|Keywords||microcantilever pulse wave actuation high-order resonant actuation laserremote actuation surface bound charge of GaN|
For the sensors with different types and functions, according to their detection mechanisms, they can be divided into electrochemical sensors, field effect transistor (FET) sensors, piezoelectric sensors, photoelectric sensors, thermal sensors and so forth. For the weak signals immerged into noises and the weak change of detected signals, how to design a sensor system with high sensitivity to extract them is one of the most important components during technology development.Recently, as the rapidly development of semiconductor technique and measurement method, it becomes reality to produce microcantilevers with micron and nanometer size. Microcantilevers’ motion can also be accurately measured. Under this background, microcantilever sensors attract a lot of scientists’and engineers’ interesting, and great achievements have been obtained. Microcantilever sensors have been wildly used in the areas of states security, food hygiene, environmental monitor, clinical medicine and so on. With the continuous advancement of technology, researches on microcantilever sensors are still to the following areas:(1) Detection via the high order resonance mode of microcantilever. The typical application is the TR scanning mode of atomic force microscopy (AFM).(2) Processing to the nanometer scale cantilever. Nano-scale cantilever features higher resonance frequencies than micron scale cantilever. Therefore, using as detector it exhibits higher detection resolution.(3) The surface modification of microcantilever beam. Through surface modification, the microcantilever responses to the adsorption of specific substance, thus the purpose of specific substance detection can be achieved.(4) Computer simulation. Nowadays, computer aided design is the indispensable tools in many areas of scientific researches and engineering applications. For the microcantilever sensors, as their scale are smaller and smaller, surface effects are more and more obvious. Furthermore, the structure of microcantilever becomes more and more complicated due to surface modification and internal structure process. All these reasons lead to the situation that the classic mechanics in most cases is difficult to solve problems, even not applicable. Therefore, it becomes one of the development trend to use computer to model and calculate microcantilever problems Current researches have confirmed that, microcantilever sensors can realize the real-time detection of weak signal in high speed and high precision. However, for a long time our country’s high precision measurement technique lags behind that of developed countries, leading to the long-term dependence on import for sophisticated equipments. which hinders the process of our country’s modernization. As the development of our country to the independent innovation country, researches on detection and recognition techniques which possess new scientific principles have become an important trend for the development of science and technology in china. The work in this thesis is carried out under the background mentioned above. Our researches is performed from the aspects of equipment construction, software development, excitation mode and application.This thesis is divided into six chapters:Chapter1:Introduction. Chapter2: Microcantilever mechanics. Chapter3:Equipments building and applications development for microcantilever vibration actuation and detection system. Chapter4: Microcantilever resonant actuation. Chapter5:Microcantilever sensor application. Chapter6:Summary and outlook. The main contents include:Chapter1:Brief introduction on microcantilever from the aspects of basic structure, mechanical characteristics, detection principle, resonant actuation methods and so on. Besides, we introduce the status of current research and the problems faced in current research. At last, we summarize the development trends of microcantilever sensor.Chapter2:Firstly, we introduce the classical theory which is used to deal with microcantilever mechanics, including the simplified one dimensional harmonic oscillator model and the rigorous "Euler-Bernoulli beam" model. Secondly, we introduce the computer simulation method which is used in the study of microcantilever sensor, i.e. the calculation for microcantilever based on the finite element method (FEM) simulation software-COMSOL Multiphysics.Chapter3:We detailed describe the hardware building and software development used for the study of microcantilever sensor. For hardware building, we realize the resonant actuation and signal detection mainly based on laser vibrometer, lock-in amplifier, and signal generator. These equipments can also work together with digital oscilloscope, data acquisition cards, and other auxiliary equipments. For software development, we write a set of application programs to realize the equipments control and data analysis. The program is written by LabVIEW, which is the most popular development environment in industrial control. All the programs are developed by ourselves, and we have got the software copyright.Chapter4:our study on microcantilever resonant actuation, including:(1) realization of resonant actuation by using pulse wave signal that has a lower frequency than microcantilever resonant frequency. The actuation mechanism is explained by Fourier analysis method. At the same time, we compare the actuation effects of pulse wave signals with different pulse duration and signals with different waveform, and we propose the solution with the best actuation effect. This result was published on Applied Physics Letters (Appl. Phys. Lett.101,061901(2012).).(2) realization of the effective actuation of the2nd-order resonation. Due to the high quality factor and improved detection resolution of high-order resonation, how to effectively actuate high-order resonation becomes one of the most important research trend for microcantilever sensor. We achieve the effective actuation of the2nd-order resonation through a relatively easy solution. This result was published on Chinese Physics Letters (Chin. Phys. Lett.30,100701(2013).).(3) realization of remote and non-contact resonant actuation for microcantilever by using modulated laser signal. For non-contact actuation, the microcantilever need not be tied to energy transducer, which provides a way for the miniaturization and integration of microcantilever sensor. Comparing with ultrasonic actuation, laser actuation has the advantages of easy focus and travelling in vacuum, which is better for improving the energy utilization ratio and achieving higher detection accuracy.Chapter5:our study on the applications of microcantilever sensor, including:(1) realization of measurement of surface bound charge for materials with self polarization, such as GaN. The measurement is based on tipless microcantilever, using the whole microcantilever surface to measure, which avoids the influence of intense electric field on charge distribution of sample induced by microcantilever tip.(2) design of field effect transistor (FET) structure with a floating gate served by microcantilever. In this work, we firstly design a method to simulate the Vds-Ids curve for traditional FET by using finite element method (FEM). And then using this method we simulate the device structure designed by ourselves. Simulation results show the feasibility of our design and how to optimize the device parameters.(3) using the results derived on microcantilever to support the conclusions obtained for laser thermal effects on quartz crystal microbalance (QCM). Currently, microcantilever and QCM are the most accurate mass detector, and they have the same detection principle. Based on this point, we use the effects of laser irradiation on microcantilever as supplementary evidence to support our conclusions of laser irradiation on QCM.Chapter6:Summarization of all the works in this thesis. Put forward the questions that should be studied in the future.The innovation of this paper include:(1) Developing the application program for resonant actuation and vibration detection of microcantilever sensor;(2) Solution of actuating microcantilever resonation with high frequency by using low frequency signal, which could be used for actuating microcantilever with super high resonant frequency;(3) Putting forward our own opinions in the areas of new actuation method such as high-order resonant actuation, remote non-contact actuation;(4) Putting forward the concept of "surface detection" in the experiment of surface bound charge measurement, improving the traditional method of "point detection";(5) Putting forward a new device design which combine microcantilever and FET.In summary, this thesis is based on the basic measurement problems in the field of nanotechnology. For the scientific and technical difficulties in microcantilever sensor, we systematically consider the aspects of mechanical, electrical, chemical, and so on, explore and analyze the related scientific and technical issues. We believe that this thesis would have important research and application values.