High Quality Factor Silicon Cantilever Driven by PZT Actuator for Resonant Based Mass Detection

A high quality factor (Q-factor) piezoelectric lead zirconat titanate (PZT) actuated single crystal silicon cantilever was proposed in this paper for resonant based ultra-sensitive mass detection. Energy dissipation from intrinsic mechanical loss of the PZT film was successfully compressed by separating the PZT actuator from resonant structure. Excellent Q-factor, which is several times larger than conventional PZT cantilever, was achieved under both atmospheric pressure and reduced pressures. For a 30 micrometer-wide 100 micrometer-long cantilever, Q-factor was measured as high as 1113 and 7279 under the pressure of 101.2 KPa and 35 Pa, respectively. Moreover, it was found that high-mode vibration can be realized by the cantilever for the pursuit of great Q-factor, while support loss became significant because of the increased vibration amplitude at the actuation point. An optimized structure using node-point actuation was suggested then to suppress corresponding energy dissipation.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Acoustic Wave Based MEMS Devices, Development and Applications

Acoustic waves based MEMS devices offer a promising technology platform for a wide range of applications due to their high sensitivity and the capability to operate wirelessly. These devices utilize acoustic waves propagating through or on the surface of a piezoelectric material. An acoustic wave device typically consists of two layers, metal transducers on top of piezoelectric substrate or thin films. The piezoelectric material has inherent capabilities of generating acoustic waves related to the input electrical sinusoidal signals placed on the transducers. Using this characteristic, different transducer designs can be placed on top of the piezoelectric material to create acoustic wave based filters, resonators or sensors. Historically, acoustic wave devices have been and are still widely used in telecommunications industry, primarily in mobile cell phones and base stations. Surface Acoustic Wave (SAW) devices are capable of performing powerful signal processing and have been successfully functioning as filters, resonators and duplexers for the past 60 years. Although SAW devices are technological mature and have served the telecommunication industry for several decades, these devices are typically fabricated on piezoelectric substrates and are packaged as discrete components. Considering the wide flexibility and capabilities of the SAW device to form filters, resonators there has been motivation to integrate such devices on silicon substrates as demonstrated in (Nordin et al., 2007; M. J. Vellekoop et al., 1987; Visser et al., 1989). One such example is illustrated in (Nordin et al., 2007) where a CMOS SAW resonator was fabricated using 0.6 m AMIs CMOS technology process with additional MEMS post-processing. The traditional SAW structure of having the piezoelectric at the bottom was inverted. Instead, the IDTs were cleverly manufactured using standard complementary-metal-oxide-semiconductor (CMOS) process and the piezoelectric layer was placed on the top. Active circuitry can be placed adjacent to the CMOS resonator and can be connected using the integrated metal layers. A SAW device can also be designed to have a long propagation path between the input and output transducer. The propagating acoustic waves will then be very sensitive to ambient changes, allowing the device to act as a sensor. Any variations to the characteristics of the propagation path affect the velocity or amplitude of the wave. Important application for acoustic wave devices as sensors include torque and tire pressure sensors (Cullen et al., 1980; Cullen et al., 1975; Pohl et al., 1997), gas sensors (Levit et al., 2002; Nakamoto et al., 1996; Staples, 1999; Wohltjen et al., 1979), biosensors for medical applications (Andle et al., 1995; Ballantine et al., 1996; Cavic et al., 1999; Janshoff et al., 2000), and industrial and commercial applications (vapor, humidity, temperature, and mass sensors) (Bowers et al., 1991; Cheeke et al., 1996; Smith, 2001; N. J. Vellekoop et al., 1999; Vetelino et al., 1996; Weld et al., 1999). In recent years, the interest in the development of highly sensitive acoustic wave devices as biosensor platforms has grown. For biological applications the acoustic wave device is integrated in a microfluidic system and the sensing area is coated with a biospecific layer. When a bioanalyte interacts with this sensing layer, physical, chemical, and/or biochemical changes are produced. Typically, mass and viscosity changes of the biospecific layer can be detected by analyzing changes in the acoustic wave properties such as velocity, attenuation and resonant frequency of the sensor. An important advantage of the acoustic wave biosensors is simple electronic readout that characterizes these sensors. The measurement of the resonant frequency or time delay can be performed with high degree of precision using conventional electronics. This chapter is focused on two important applications of the acoustic-wave based MEMS devices; (1) biosensors and (2) telecommunications. For biological applications these devices are integrated in a microfluidic system and the sensing area is coated with a biospecific layer. When a bioanalyte interacts with this sensing layer, physical, chemical, and/or biochemical changes are produced. Typically, mass and viscosity changes of the biospecific layer can be detected by analyzing changes in the acoustic wave properties such as velocity, attenuation and resonant frequency of the sensor. An important advantage of the acoustic wave biosensors is simple electronic readout that characterizes these sensors. The measurement of the resonant frequency and time delay can be performed with high degree of precision using conventional electronics. Only few types of acoustic wave devices could be integrated in microfluidic systems without significant degradation of the quality factor. The acoustic wave based MEMS devices reported in the literature as biosensors are film bulk acoustic wave resonators (FBAR) and surface acoustic waves (SAW) resonators and SAW delay lines. Different approaches to the realization of FBARs and SAW resonators and SAW delay lines used for various biochemical applications are presented. Next, acoustic wave MEMS devices used in telecommunications applications are presented. Telecommunication devices have different requirements compared to sensors, where acoustic wave devices operating as a filter or resonator are expected to operate at high frequencies (GHz), have high quality factors and low insertion losses. Traditionally, SAW devices have been widely used in the telecommunications industry, however with advancement in lithographic techniques, FBARs are rapidly gaining popularity. FBARs have the advantage of meeting the stringent requirement of telecommunication industry of having Qs in the 10,000 range and silicon compatibility

On the nonlinear dynamics of a piezoresistive based mass switch based on catastrophic bifurcation

This research investigates the feasibility of mass sensing in piezoresistive MEMS devices based on catastrophic bifurcation and sensitivity enhancement due to the orientation adjustment of the device with respect to the crystallographic orientation of the silicon wafer. The model studied is a cantilever microbeam at the end of which an electrostatically actuated tip mass is attached. The piezoresistive layers are bonded to the vicinity of the clamped end of the cantilever and the device is set to operate in the resonance regime by means of harmonic electrostatic excitation. The nonlinearities due to curvature, shortening and electrostatic excitation have been considered in the modelling process. It is shown that once the mass is deposited on the tip mass, the system undergoes a cyclic fold bifurcation in the frequency domain, which yields a sudden jump in the output voltage of the piezoresistive layers; this bifurcation is attributed to the nonlinearities governing the dynamics of the response. The partial differential equations of the motion are derived and discretized to give a finite degree of freedom model based on the Galerkin method, and the limit cycles are captured in the frequency domain by using the shooting method. The effect of the orientation of the device with respect to the crystallographic coordinates of the silicon and the effect of the orientation of the piezoresistive layers with respect to the microbeam length on the sensitivity of the device is also investigated. Thanks to the nonlinearity and the orientation adjustment of the device and piezoresistive layers, a twofold sensitivity enhancement due to the added mass was achieved. This achievement is due to the combined amplification of the sensitivity in the vicinity of the bifurcation point, which is attributed to the nonlinearity and maximizing the sensitivity by orientation adjustment of the anisotropic piezoresistive coefficients

Real-Time Bio Sensing Using Micro-Channel Encapsulated MEMS Resonators

This work presents a label-free bio-molecular detection technique based on realtime monitoring of the resonant frequency of micromechanical thermal-piezoresistive rotational mode disk resonators encapsulated in microfluidic channels. Mass loading via adsorption of molecular layers on the surface of such devices results in a frequency shift. In order to provide a reliable platform for sample-resonator interactions and to protect the resonators from contaminants, the resonators were encapsulated in PDMS-based microfluidic channels. Micro-channel encapsulation also allows insulation of electrical signals from the analyte solution. To characterize the performance of such devices as real-time label-free bio-molecular detectors, the strong non-covalent binding of Avidin with its ligand, biotin was utilized. To further validate the measured frequency shifts and confirm that the frequency shifts are due to molecular attachments to the resonator surfaces, fluorescent labeled molecules followed by fluorescent imaging was used confirming the existence of the expected molecular layers on the resonator surfaces

Design, Simulation And Analysis Of Piezoresistive Microcantilever For Biosensing Applications

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2016Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2016Son on yılda, çeşitli araştırma çalışmaları, Biyolojik Mikroelektromekanik Sistem (Bio-MEMS) biyosensörlerinin Deoksiribonükleik Asit (DNA), proteinler, Bakteri ve Antijenler gibi biyomolekülleri belirleme yeteneğini ortaya koydu. Ancak, numunelerde tespit edilmesi gereken analitlerin düşük konsantrasyonundan dolayı, sensörün çıktısına ufak bir sinyal neden olur. Buna cevap olarak, numunedeki birkaç analitin bulgulanmasına yanıt olarak yüksek çıktı sinyali verebilen optimize edilmiş bir biyosensör için bir ihtiyaç ortaya çıkmıştır; Nihai hedef tek bir biyomoleküle yapışmayı ölçülebilir bir miktara dönüştürmektir. Bu amaçla, basit, ucuz, oldukça hassas ve daha önemlisi analitlerin optik etiketlenmesine ihtiyaç duymadığı için (Etiketsiz), MEMS mikrokantilever tabanlı biyosensörler umut verici bir algılama çözümü olarak ortaya çıkmıştır. Farklı mikrokandilever ileten teknikler arasında, piezoresistif tabanlı mikrokantilever biyosensörler, ucuz, yüksek hassasiyetli, minyatür olan, sıvı ortamlarda iyi çalışan ve entegre okuma sistemi olan cazip bir çözüm gibi gözükmektedir. Literatürde piezoresistif mikrokolantların hassasiyetini arttırmaya odaklanan birçok yayın olmasına rağmen, sırf birkaç tasarım ve işlem parametresini optimize etmeyi düşündükleri için sonuçta elde edilen hassaslık arttırmaları pratik uygulamalar için yetersiz kalıyordu. Literatürde yapılan çalışmanın analizinden sonra, Piezoresistif mikrokandilöre dayalı sensörlerin hassasiyetini arttırmak için optimize edilebilen / kullanılabilen parametreler / yaklaşımlar: kantilever boyutları, kantilever Malzemesi, kantilever şekli, Piezoresistör malzemesi, Piezoresistör Doping seviyesi, Piezoresistör Boyutları, Piezoresistörün konumu, Stres konsantrasyon Bölgesinin (SCR) şekli ve konumu. Bu çalışmada, tüm tasarım ve işlem parametrelerinin duyarlılık üzerindeki etkisini analizi yapıldıktan sonra, kademeli optimizasyon yaklaşımı geliştirilmiş. Bu yaklaşımında neredeyse tüm parametreleri , her adımda biri olmak üzere, değiştirerek öbtimsyon yapılmış ve öyleyse hassasiyet maksimum düzeyde olmasını sağlamıştır. Bu çalışma boyunca, sensör performansını simüle etmek için ticari bir Sonlu Elemanlar Analizi (FEA) aracı olan COMSOL Multiphysics 5.0 kullanıldı. Her bir optimizasyon adımında, aynı uygulanan kuvvet için piezoresistor bölgelerindeki gerilimi en üst düzeye çıkaracak ve yoğunlaştıracak şekilde parametrenin optimize edilmesi hedefi daha yüksek duyarlılık elde etmektir. Toplamda, son optimize edilmiş sensörü elde etmek için neredeyse 46 farklı simülasyon yapıldı. Biyolijik uygulamalarında kullanılan etkileşimli kuvvetler onlarca ila yüzlerce pN arasında olduğu için, bu sensörde kullanılacak 25 ila 250 pN aralığı seçilmiştir. Optimizasyon işlemindeki tüm simülasyonlar sırasında 250 pN'lik bir toplam xxvi dağıtılmış kuvvet, analitlerin sensöre bağlanmasını temsil eden Altın katmanın üzerine uygulanır. Başlangıç olarak sırasıyla uzunluk, genişlik ve kalınlık için boyutları (200μm × 120μm × 1.5μm) olan dikdörtgen bir tek kristal Silicon Microcantilever kullanılmıştır. Konsolun üst kısmında, analitlerin tutturulması için 100μm × 100μm × 0.2μm Gold katmanı kullanılırken, piezo rezistanslı algılama için 20μm × 5μm × 0.5μ dikdörtgen polisilik piezoresistor kullanılır. Burada kullanılan piezoresistor, 1 x 1016 cm-3 'lük bir p-tipi dopant yoğunluğuna, 400 nm'lik bir kalınlığa ve 1V'lık uyarılma voltajına sahiptir. Dikdörtgen bir konsoldan başlamak üzere piezoresistor malzemesi ve doping seviyesi iki aşamada optimize edilmiştir. Piezistoristor malzemesi değiştiğinde (tek kristal silikon ve Poly-silikon), tek kristal silikon durumunda ΔR / R duyarlılığının daha yüksek olduğu bulundu. Fakat bu sensör tasarımı için, hassasiyet kristal yönüne bağlı olmayan, sensör imalatı daha kolay, daha ucuz ve ITUnano laboratuarında gerçekleştirilebildiğinden, piezoresistor malzemesi olarak polisilikon seçilmiştir. Sonra, doping düzeyini 1 x 1015 cm-3 ile 1 x 1020 cm-3 aralığında değiştirerek ve ΔR / R hassasiyetini hesaplayarak, aşağıdaki simülasyonlar boyunca kullanılacak doping seviyesi belirlendi. 1 × 1018 cm -3 doping seviyesinin, termal gürültü etkisini azaltacak kadar yüksek olduğu, aynı zamanda duyarlılığın da o kadar fazla etkilemediği görülmektedir. Böylece, bu doping seviyesi tüm sonrakı simülasyonlar boyunca seçildi ve kullanıldı. Daha sonra konsol malzemesi, aynı uygulanan kuvvet için maksimum gerilme ve sapma sağlayan malzeme bulmak için çeşitlendirilir. Beklendiği gibi, farklı konsol malzemeler, farklı maksimum sapma ve gerilme değerleri verdi. Elde edilen bulgulara göre, Silikon Dioksit (SiO2) düşük genç modül değerleri nedeniyle diğer malzemelere kıyasla en yüksek azami sapma ve gerilme değerlerine sahip olduğu bulundu.Tekli kristal silikon (başlangıç konsol malzemesi) durumunda olduğu gibi SiO2'nin neredeyse 2.5 kat daha yüksek sapma ve 1.7 kat daha yüksek hassaslık ile sonuçlandı ve böylece bu biyosensörün konsol malzemesi olarak SiO2 seçildi ve aşağıdaki optimizasyon adımlarda kullanıldı. Daha sonra, çeşitli konsol şekilleri (Dikdörtgen, Pi-şekli, T-şekli, Trapezoid, Kademeli-Trapezoid ve Üçgen) tanıtıldı ve her şekil için boyutlar, işlem ve cihaz sınırlamaları göz önünde bulundurularak değiştirildi. Bütün bu simülasyonların sonuçları, maksimum hassaslığı veren optimize şekli bulmak için karşılaştırıldı. Dikdörtgen şekil mikrokantilever optimizasyon adımı sırasında konsol kalınlığının konsol uzunluğu ve genişliğindeki değişimle karşılaştırıldığında sensör hassasiyeti üzerinde en yüksek etkiye sahip olduğu bulunmuştur. Konsol kalınlığı 3μm ve 1.5μm arasında değiştiğinde, konsol kalınlığı azaldığında duyarlılık arttığı bulundu. 1.5μm kalınlıktaki konsolun kullanılması, 3μm kalınlıktaki konsoldan 4 kat daha fazla yüksek hassasiyet göstermiştir. Böylece, 1.5μm son optimize konsol kalınlığı olarak seçildi. Konsol uzunluğu 150μm ila 350μm arasında değiştirildiğinde, konsol uzunluğu arttıkça hassasiyet artmaktadır. Elde edilen sonuçlara göre, 350μm uzunluğunda konsolun 150μm uzunluğundaki konsoldan yaklaşık 3.5 kat daha yüksek bir xxvii hassaslık verdiğini görüyoruz. Böylece, 350μm son optimize konsol uzunluğu olarak seçildi. Konsol genişliği 120μm ve 250μm arasında değiştirildiğinde, konsol genişliği arttıkça hassasiyet azalmaktadır. Elde edilen sonuçlara göre, 120μm genişlikli konsolun 250μm genişliğinde konsoldan 2.4 kat daha yüksek bir hassaslık verdiğini görüyoruz. Böylece, 120μm son optimize konsol genişliği olarak seçildi. Buna ek olarak, farklı dikdörtgen mikrokantilever boyutları optimize edildikten sonra (uzunluk, genişlik ve kalınlık), duyarlılık 18.3x kat arttı. Ayrıca, dikdörtgen konsol yapısına (T şekli) iki yan delik eklenmesi, duyarlılığı 1,6 oranında arttırmıştır. Farklı trapezoid biçimli konsollardan elde edilen sonuçlardan, sıkıştırılmış konsol kenarı ile serbest kenar arasındaki 1:4 oranındaki yapının en yüksek maksimum von Mises stresini ve en yüksek duyarlılığı verdiğini görülebilir. Bunların 1:1'lik durumundan (optimize edilmiş dikdörtgen konsol) neredeyse 2.5 kat daha fazla hassasiyet vardır. Böylece, bu tasarım optimize edilmiş yamuk şeklinde konsol tasarımı olarak seçildi. Farklı basamaklı trapezoid şekilli konsollardan elde edilen sonuçlara göre, sıkıştırılmış konsol kenarı ile serbest kenara arasındaki oran 1: 4 olan yapıda, en yüksek maksimum von Mises gerilmesi ve en yüksek duyarlılık görülürken, bunun neredeyse 2.5 kat arttığı görülmektedir 1: 1'den daha büyüktür (optimize edilmiş dikdörtgen konsol). Böylece, bu tasarım optimize edilmiş basamaklı trapez şeklinde konsol tasarımı olarak seçildi. Aynı uygulanan kuvvet için, trapez şeklinde mikrokancilever tasarımı, başlangıç sensöründen 46 kat daha fazla daha yüksek hassasiyet vermiştir Hassasiyet), Kademeli-Trapezoid şekli en fazla azami sapma göstermiştir. Ardından, daha fazla duyarlılık geliştirme arayışında olan farklı konum ve yönlerde optimize trapezoid yapıda Stres Yoğunlaştırma Bölgesi (SCR) tanıtıldı. Simülasyonlardan, kelepçelenmiş konsol kenarından 15μm uzakta bulunan optimize edilmiş trapezoid yapıya 30μ × 10μm SCR dikdörtgen bir delik açılmasının, diğer konumlara kıyasla en iyi hassasiyet değerini veren neredeyse 1.6x kat daha fazla hassasiyet artışı sağladığı bulundu. Nihai sensör duyarlılığı, uygulanan kuvvete karşı dirençteki normalize edilmiş değişim açısından -1.5×10-8 Ω/Ω ⁄pN 'ye eşittir. Bu, her bir 1pN (10-10 g) için biyomoleküllerin bu biyosensöre tutunması için, piezoresistor direnci 1.5×10-8 Ω kadar azalacaktır. Başlangıç sensörüne kıyasla, son sensör tasarımı 73.5x kat daha iyi ΔR / R duyarlılığı sağlamış ve daha önce literatürde bildirilen diğer sensör tasarımlarına göre daha duyarlıdır. Bu sensörün üretim sırası hazırlanmış ancak ITUnano laboratuvarında bulunan bazı cihazlarda teknik problemler nedeniyle sensör üretilmemiştir. Gelecekteki bir çalışma olarak, önerilen imalat dizisi sensörü imal etmek ve sonuçları simülasyon sonuçları ile karşılaştırmak için kullanılacaktır. Simülasyon sonuçlarına göre, konsol kalınlığı ve piezoresistor kalınlığı sensör hassasiyetini kolayca etkiler. Bu tasarımda silisyum dioksit konsol ve polisilikon piezoresistor için en düşük kalınlık sınırı olarak 1.5μm ve 0.5μm ayarlandı. Aynı tasarım için bu malzemelerin daha ince katmanlarının kullanılması duyarlılığın daha da artmasına neden olacaktır.In the past decade, several research works demonstrated the ability of Biological Microelectromechanical System (Bio-MEMS) biosensors to detect of biomolecules such as Deoxyribonucleic Acid (DNA), proteins, Bacteria and Antigens. But due to the low concentration of the analytes that need to be detected in the samples,a minuscule signal results in the output of the sensor. In response to this, a need arisen for an optimized biosensor capable of giving high output signal in response the detection of few analytes in the sample; the ultimate goal is being able to convert the attachment of a single biomolecule into a measurable quantity. For this purpose, MEMS microcantilevers based biosensors have emerged as a promising sensing solution because it is simple, cheap, highly sensitive and more importantly does not need analytes optical labeling (Label-free). Among the different microcantilever transducing techniques, piezoresistive based microcantilever biosensors seem to be a more attractive solution being cheap, high sensitive, miniature, works well in liquid environments and having integrated readout system. Even though there are many publications in literature that concentrated on increasing the piezoresistive microcantilevers sensitivity, they only considered in optimizing few design and process parameters thus the resultant sensitivity enhancements are not good enough for practical applications. After the analyzation of the work found in literature, it was found that the parameters/approaches that be can be optimized/used to enhance the sensitivity of Piezoresistive microcantilever-based sensors are: Cantilever dimensions, Cantilever Material, Cantilever Shape, Piezoresistor's material, Piezoresistor's doping level, Piezoresistor's Dimensions, Piezoresistor's position, Stress concentration Region's (SCR) shape and position. In this study, after a systematic analyzation of the effect of each design and process parameters on the sensitivity, a step-wise optimization approach was developed in which almost all these parameters were variated one at each step while fixing the others to get the maximum possible sensitivity at the end. Throughout this work, COMSOL Multiphysics 5.0, a commercial Finite Element Analysis (FEA) tool, was used to simulate the sensor performance. At each optimization step, the goal was to optimize the parameter in such a way that it maximizes and concentrates the stress in piezoresistors region for the same applied force thus get the higher sensitivity. In total, almost 46 different simulations were done to get the final optimized sensor. Starting with a rectangular cantilever, the piezoresistor material and doping level were optimized in two steps. When the piezoresistor material was varied (single crystal silicon and Poly-silicon), it was found that the ΔR⁄R sensitivity is higher in the case of single crystal silicon. xxiv But for this sensor design, polysilicon has been chosen as the piezoresistor material because it’s sensitivity does not depend on the crystal orientation, the sensor fabrication is easier, cheaper and can be realized in ITUnano laboratory. Next, by changing the doping level in the range between 1×1015 cm−3 to 1×1020 cm−3 and calculating the ∆R/R sensitivity, the doping level that will be used throughout the following simulations was determined. It was found that, 1×1018 cm−3 doping level is high enough to reduce the thermal noise effect, at the same time it does not be affected the sensitivity that much. Thus this doping level was chosen and used throughout the following simulations. Afterward, the cantilever material is varied to find the material that gives maximum stress and deflection for the same applied force. It was found that SiO2 resulted into almost 2.5x higher deflection and 1.7x higher sensitivity when compared to single crystal silicon (the starting cantilever material) case thus SiO2 has been selected as the cantilever material for this biosensor and it is used in the following optimization steps. Next, various cantilever shapes (Rectangular, Pi-shape, T-shape, Trapezoid, SteppedTrapezoid, and Triangular) were introduced, and for each shape, the dimensions were varied bearing in mind the process and device limits. The results from all these simulations were compared to find the optimized shape which gives the maximum sensitivity. During the rectangular shape microcantilever optimization step, it was found that the cantilever thickness has the highest effect on the sensor sensitivity when compared to the change in cantilever length and width. In addition to that, after the different rectangular microcantilever dimensions were optimized (length, width and thickness), the sensitivity increased 18.3x folds. Also, adding two side holes to the rectangular cantilever structure (T-shape) increased the sensitivity by 1.6 factor. Overall, for the same applied force, the trapezoid-shaped microcantilever design gave higher sensitivity (more than 46x times greater than the starting sensor sensitivity) whereas the stepped-trapezoid shaped gave the highest maximum deflection. Afterward, Stress Concentration Region (SCR) was introduced in the optimized trapezoid structure in different locations and orientations seeking for further sensitivity enhancement. From the simulations, it was found that adding a 30µ×10µm SCR rectangular hole to the optimized trapezoid structure 15µm away from the clamped cantilever edge, resulted in almost 1.6x times sensitivity enhancement which gave the best sensitivity value compared to the other positions. Regarding the normalized change in resistance to the applied force the final sensor’s sensitivity equals to -1.5×10-8 Ω/Ω ⁄pN; this means that for each 1pN (10-10 g) biomolecules attach to this biosensor; the piezoresistor resistivity will decrease by 1.5×10-8 Ω. When compared to the starting sensor, the final sensor design gave 73.5x times better ΔR⁄R sensitivity and it is more sensitive than the other sensor designs previously reported in the literature. The fabrication sequence for this sensor was prepared, but due to technical problems in some of the devices found in ITUnano laboratory, the sensor has not been fabricated.Yüksek LisansM.Sc

Piezoelectric amplifiers with integrated actuation and sensing capabilities

We report in this work on unprecedented levels of parametric amplification in microelectromechanical systems (MEMS) resonators with integrated piezoelectric actuation and sensing capabilities operated in air. The method presented here relies on accurate analytical modeling taking into account the geometrical nonlinearities inherent to the bridge-like configuration of the resonators used. The model provides, for the first time, precise analytical formula of the quality factor (Q) enhancement depending on the resonant mode examined. Experimental validations were conducted for resonant modes exhibiting, respectively, hard and soft-spring effects when driven in the nonlinear regime; Q amplification by a factor up to 14 has been obtained in air

Simulation of a surface transverse wave biosensor for DF-1 cells

A 250MHz Surface-Transverse Wave (STW) resonator is employed as a sensor element for the detection of DF-1 cells. STWs are horizontally polarized shear waves which are generated and detected by the interdigitated transducers (IDTs) similar to surface-acoustic wave (SAW) resonators. Detection of chemical and biological agents in aqueous solutions is a difficult problem, especially when the detection technique has to be sensitive, power-efficient and very handy. This paper presents the biosensor prototype utilizing STW resonator. The two-dimensional finite element (FEM) modeling of the STW resonator was performed using COMSOL Multiphysics #x2122;. 200MHz operating frequency was applied in the simulation. The FEM simulations results are equal with the theoretical results where an operating frequency of 200MHz will produce a resonance frequency of 200MHz

Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications

Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications

Development of a PDMS Based Micro Total Analysis System for Rapid Biomolecule Detection

The emerging field of micro total analysis system powered by microfluidics is expected to revolutionize miniaturization and automation for point-of-care-testing systems which require quick, efficient and reproducible results. In the present study, a PDMS based micro total analysis system has been developed for rapid, multi-purpose, impedance based detection of biomolecules. The major components of the micro total analysis system include a micropump, micromixer, magnetic separator and interdigitated electrodes for impedance detection. Three designs of pneumatically actuated PDMS based micropumps were fabricated and tested. Based on the performance test results, one of the micropumps was selected for integration. The experimental results of the micropump performance were confirmed by a 2D COMSOL simulation combined with an equivalent circuit analysis of the micropump. Three designs of pneumatically actuated PDMS based active micromixers were fabricated and tested. The micromixer testing involved determination of mixing efficiency based on the streptavidin-biotin conjugation reaction between biotin comjugated fluorescent microbeads and streptavidin conjugated paramagnetic microbeads, followed by fluorescence measurements. Based on the performance test results, one of the micromixers was selected for integration. The selected micropump and micromixer were integrated into a single microfluidic system. The testing of the magnetic separation scheme involved comparison of three permanent magnets and three electromagnets of different sizes and magnetic strengths, for capturing magnetic microbeads at various flow rates. Based on the test results, one of the permanent magnets was selected. The interdigitated electrodes were fabricated on a glass substrate with gold as the electrode material. The selected micropumps, micromixer and interdigitated electrodes were integrated to achieve a fully integrated microfluidic system. The fully integrated microfluidic system was first applied towards biotin conjugated fluorescent microbeads detection based on streptavidin-biotin conjugation reaction which is followed by impedance spectrum measurements. The lower detection limit for biotin conjugated fluorescent microbeads was experimentally determined to be 1.9 x 106 microbeads. The fully integrated microfluidic system was then applied towards immuno microbead based insulin detection. The lower detection limit for insulin was determined to be 10-5M. The total detection time was 20 min. An equivalent circuit analysis was performed to explain the impedance spectrum results

Application of cantilever-based microbiosensors in microbiology

This paper presents applications of cantilever-based microbiosensors in microbiology and other biological fields. These devices can be employed in a wide range of experiments due to their high sensitivity and capability of performing label-free and real-time measurements. Cantilever-based microbiosensors are employed in a variety of measurements, such as single cell mass, concentration of specific substances, their density and viscosity, fluid flow velocity, heat of reaction or detection of trace amounts of specified substances. All these applications ares possible, because cantilever surface can be specifically functionalized. In the last few years, the cantilever-based microbiosensors have been significantly improved to obtain even higher precision of measurement which allows for their new, unique applications with live biological system