Gerilme Tabanlı Kendiliğinden Birleşme:Mikro Nano Entegrasyonunda Kırılma Mekaniği Uygulamaları

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Katmanlı yapılarda gözlemlenen kırılma, yapı üzerinde etkili olan mekanik gerilimlerin doğasına bağlı olarak çeşitli çatlak şekillerine yol açmaktadır. Çatlakların gerek açıklıkları gerek yönleri, tamamen katmanlı yapı özellikleri ve gerilimlerin uygulanış biçimine bağlı olarak numuneden numuneye tekrar edilebilir şekilde gözlemlenebilir. Bunun sonucunda gerilimleri kontrol ederek çatlak yönlerini tayin etme fırsatı ortaya çıkmaktadır. Yön tayini, ilk önce tek kristal yapıya sahip Si alttaş üzerindeki ince SiO2 kaplamalarında gösterilmiştir. Alttaşın derin reaktif iyon aşındırması gibi tekniklerle mikro boyutta şekillendirilmesi ile tayin edilen gerilim dağılımı, aynı anda binlerce çatlağın deterministik bir şekilde oluşmasını sağlamaktadır. Ayrıca çatlak açıklıklarının nano mertebesinde olması ve çatlağın SiO2 ve Si arayüzünde durması sayesinde, çatlakların ikinci bir malzeme ile doldurulmaları, nanotel imalatını mümkün kılmaktadır. Böylece çatlak ağı, bir nanotel ağına dönüştürülür. Yonga üzerinde her çatlağın başlangıç noktasının koordinatı ve yönü bilindiği için üst yapıların litografi kullanılarak bu nanotel ağına göre hizalanması mümkün olmaktadır. Bu tür bir sistem entegrasyonu, mikro bir tahrik mekanizmasının iki nanotele göre hizalanarak imaline dayalı bir cımbız cihazının bünyesinde gerçekleştirilmiştir. Çalışma, nanoteknolojinin büyük ihtiyaçlarından biri olan, nano yapıların kontrollü imalatına yönelik olup, uygulamalı mekaniğin bu alanda üstlenebileceği role işaret etmektedir.Various crack patterns are observed in multilayers depending on the nature of applied stresses. Crack opening and propagation paths can be obtained in a repeatable fashion if multilayer material properties and the stress state are precisely controlled. This leads to the possibility of dictating crack paths by controlling the stress state, which was first demonstrated on SiO2-coated Si samples. By patterning the Si substrate through deep reactive ion etching one can determine the distribution of stresses and dictate the simultaneous formation of thousands of cracks. Furthermore, since crack openings are at nanoscale and they arrest at the substrate/thin film interface, one can fill the cracks with a second material and obtain nanowires. Hence, a network of cracks is transformed into a network of nanowires. Since one knows the coordinates of the initiation point of cracks and their orientation, one can easily align subsequent lithography steps with respect to the existing nanowires. This aspect of system integration is demonstrated in the case of a gripper device with two nanoscale endeffectors attached at the tip of a microscale actuator. The study addresses the issue of controlled fabrication of nanostructures, one of the main issues faced by nanotechnology, and the role that applied mechanics can play in this field

Mechanical Properties of Silicon Nanowires with Native Oxide Surface State

Silicon nanowires have attracted considerable interest due to their wide-ranging applications in nanoelectromechanical systems and nanoelectronics. Molecular dynamics simulations are powerful tools for studying the mechanical properties of nanowires. However, these simulations encounter challenges in interpreting the mechanical behavior and brittle to ductile transition of silicon nanowires, primarily due to surface effects such as the assumption of an unreconstructed surface state. This study specifically focuses on the tensile deformation of silicon nanowires with a native oxide layer, considering critical parameters such as cross-sectional shape, length-to-critical dimension ratio, temperature, the presence of nano-voids, and strain rate. By incorporating the native oxide layer, the article aims to provide a more realistic representation of the mechanical behavior for different critical dimensions and crystallographic orientations of silicon nanowires. The findings contribute to the advancement of knowledge regarding size-dependent elastic properties and strength of silicon nanowires.Comment: 11 pages, 10 figure

Determination of mechanical properties of different sized silicon and silica nanowires tested in SEM

To push miniaturization in electronics forward, integration of silicon or silica nanowires into microelectromechanical based sensors (MEMS) becomes essential, because they were found to enhance the overall sensitivity and noise immunity. With respect to mechanical stress may develop in nanowires in operation of the MEMS system, their stability need to be checked to ensure long-term reliability. The monolithic fabrication includes a controlled two-step chip-on-wafer etching technique resulting in double-anchored wires with the minimum width of 35 nm, the maximum width of 74 nm and a height of 168 nm with clamped wire endings for silicon [1,2]. Based on this idea clamped silica wires with widths between 150 to 200 nm and heights of 50 nm and 372 nm were created due to prior coating of a silicon bulk with a silsesquioxane precursor in addition to subsequent e-beam irradiation [3]. Dimensions and shape of the wire cross-sections were exemplary investigated using transmission electron microscopy, while the determination of the respective wire´s length between the clamped endings of 2 to 12µm and the in-situ three-point-bending tests were carried out within a scanning electron microscope. A micromanipulator equipped with a piezo-resistive force sensor, shaped like a cantilever conventionally used for atomic force microscopes was loaded and unloaded at the wires mid-span and forces were detected. Simultaneously the systematic tests were recorded in scanning electron micrographs taken each second to extract force-displacement (f-d) curves of the different sized nano-objects. As expected for brittle material, silicon nanowires showed well-known f-d behavior. Considering a modulus of elasticity of 169 GPa for bulk [100] silicon and the influence of the native oxide finite element simulation (FEM) exactly fit to the experimental data leading to the conclusion that no size dependence for elastic properties was identified [4]. Same observations were made with silica wires until a stress level of about 0.1 to 0.4 GPa is reached and a superplastic deformation without fracture of the wires takes place. The validation of the f-d results from the systematic study of the fracture behavior of silicon wire is in progress. Due to the special wire geometry (small width in relation to height) buckling occurs during loading, implemented within a finite-element simulation, which needs still further refinement. Finally, this study will help to predict mechanical behavior (or vice versa the dimensions) of MEMS integrated silicon nanowires. The project leading to this application has received funding from the EMPIR programme Strength-ABLE co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme. [1] Z. Tasdemir, N. Wollschläger, W. Österle, Y. Leblebici and B. E. Alaca: A deep etching mechanism for trench-bridging silicon nanowires, Nanotechnology 27 (2016) 095303. [2] M. Yilmaz, Y. Kilinc, G. Nadar, Z. Tasdemir, N. Wollschläger, W. Österle, Y. Leblebici and B. E. Alaca: Top-down technique for scaling to nano in silicon MEMS, J. Vac. Sci. Technol. B 35 (2017) 022001-1 [3] M. Yilmaz, N. Wollschläger, M. Nasr Esfahani, Österle, Y. Leblebici and B. E. Alaca: Superplastic behavior of silica nanowires obtained by direct patterning of silsesquioxane-based precursors, Nanotechnology 28 (2017) 115302. [4] N. Wollschläger, Z. Tasdemir, I. Häusler, Y. Leblebici, W. Österle and B. E. Alaca: Determination of the Elastic Behavior of Silicon Nanowires within a Scanning Electron Microscope, J. Nanomat. (2016) 4905838-

Mechanical Properties of Silicon Nanowires with Native Oxide Surface State

Silicon nanowires have attracted considerable interest due to their wide-ranging applications in nanoelectromechanical systems and nanoelectronics. Molecular dynamics simulations are powerful tools for studying the mechanical properties of nanowires. However, these simulations encounter challenges in interpreting the mechanical behavior and brittle to ductile transition of silicon nanowires, primarily due to surface effects such as the assumption of an unreconstructed surface state. This study specifically focuses on the tensile deformation of silicon nanowires with a native oxide layer, considering critical parameters such as cross-sectional shape, length-to-critical dimension ratio, temperature, the presence of nano-voids, and strain rate. By incorporating the native oxide layer, the article aims to provide a more realistic representation of the mechanical behavior for different critical dimensions and crystallographic orientations of silicon nanowires. The findings contribute to the advancement of knowledge regarding size-dependent elastic properties and strength of silicon nanowires

Stencil lithography for bridging MEMS and NEMS

The damage inflicted to silicon nanowires (Si NWs) during the HF vapor etch release poses a challenge to the monolithic integration of Si NWs with higher-order structures, such as microelectromechanical systems (MEMS). This paper reports the development of a stencil lithography-based protection technology that protects Si NWs during prolonged HF vapor release and enables their MEMS integration. Besides, a simplified fabrication flow for the stencil is presented offering ease of patterning of backside features on the nitride membrane. The entire process on Si NW can be performed in a resistless manner. HF vapor etch damage to the Si NWs is characterized, followed by the calibration of the proposed technology steps for Si NW protection. The stencil is fabricated and the developed technology is applied on a Si NW-based multiscale device architecture to protectively coat Si NWs in a localized manner. Protection of Si NW under a prolonged (>3 h) HF vapor etch process has been achieved. Moreover, selective removal of the protection layer around Si NW is demonstrated at the end of the process. The proposed technology also offers access to localized surface modifications on a multiscale device architecture for biological or chemical sensing applications

On heat transfer at microscale with implications for microactuator design

The dominance of conduction and the negligible effect of gravity, and hence free convection, are verified in the case of microscale heat sources surrounded by air at atmospheric pressure. A list of temperature-dependent heat transfer coefficients is provided. In contrast to previous approaches based on free convection, supplied coefficients converge with increasing temperature. Instead of creating a new external function for the definition of boundary conditions via conductive heat transfer, convective thin film coefficients already embedded in commercial finite element software are utilized under a constant heat flux condition. This facilitates direct implementation of coefficients, i.e. the list supplied in this work can directly be plugged into commercial software. Finally, the following four-step methodology is proposed for modeling: (i) determination of the thermal time constant of a specific microactuator, (ii) determination of the boundary layer size corresponding to this time constant, (iii) extraction of the appropriate heat transfer coefficients from a list provided and (iv) application of these coefficients as boundary conditions in thermomechanical finite element simulations. An experimental procedure is established for the determination of the thermal time constant, the first step of the proposed methodology. Based on conduction, the proposed method provides a physically sound solution to heat transfer issues encountered in the modeling of thermal microactuators

Mikroskop İle Tümleştirilmiş Tek Eksenli Çekme Cihazı İle Pdms’nin Viskoelastik Karakterizasyonu

Konferans Bildirisi-- İstanbul Teknik Üniversitesi, Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2017Conference Paper -- İstanbul Technical University, Theoretical and Applied Mechanical Turkish National Committee, 2017Polidimetilsiloksan (PDMS) ayarlanabilir mekanik ve yüzey özellikleri sayesinde biyomedikal, ilaç taşıyıcı sistemler, mikroakışkan çalışmalar ve biyolojik algılayıcılarda sıklıkla kullanılmaktadır. Günümüzde PDMS kullanılarak kontrollü bir şekilde mikron-altı (submicron) boyutta yapılar inşa edilmekte ve bu yapılar kullanılarak nanoNewton-altı kuvvetler ölçülebilmektedir. PDMS yapılardaki deformasyonları doğru bir şekilde kuvvet değerlerine çevirmek için PDMS’ye en uygun bünye (constitutive) modelin oluşturulması gerekmektedir. Doğrusal olmayan mekanik özelliklere sahip PDMS’nin detaylı bir karakterizasyonu yapılmış olmasına rağmen Poisson oranı rapor edilirken PDMS’nin viskoelastik özelliği hesaba katılmamıştır. PDMS için literatürde belirtilen Poisson oranı 0.45 ile 0.5 arasında değişmektedir. Poisson oranının kullanılan gerinim tanımından bağımsız ve statik şartlarda raporlanması eksik ve hatalı bir ifadedir. PDMS için detaylı bir Poisson oranı incelemesi içeren bu çalışmada tek eksenli bir çekme düzeneği optik mikroskop ile tümleştirilerek çekme esnasında test numunesinin belirli bölgelerinden mikroskop görüntüleri alınmıştır. Poisson oranını doğru ve eksiksiz olarak tanımlamak için PDMS’nin viskoelastik özelliği ve kullanılacak gerinim tanımları hesaba katılmıştır.Polydimethylsiloxane (PDMS) is frequently used in drug delivery systems, microfluidic devices, biomedical systems and biosensors due to its tunable mechanical and surface properties. In recent studies, the traction forces in sub-nanoNewton were measured by interpreting the deformation of PDMS micropillars which are precisely patterned at the submicron scale. Although PDMS is a well-known viscoelastic material, researchers did not take viscoelastic properties into account while reporting Poisson’s ratio. The reported Poisson’s ratio for PDMS varies between 0.45 and 0.50 and is considered time-independent despite of its viscoelasticity. Defining Poisson’s ratio as a constant without referring to any strain definition provides an incomplete and incorrect picture. In this study, a detailed study of Poisson’s ratio of PDMS will be carried out by integrating a uniaxial tensile stretcher with an optical microscope to capture images of a certain area in the field of view during stretching. We took viscoelastic properties of PDMS and strain definition into account to make a complete and proper definition of Poisson’s ratio

Monolithic Integration of Silicon Nanowires With a Microgripper

Si nanowire (NW) stacks are fabricated by utilizing the scalloping effect of inductively coupled plasma deep reactive ion etching. When two etch windows are brought close enough, scallops from both sides will ideally meet along the dividing centerline of the windows turning the separating material column into an array of vertically stacked strings. Upon further thinning of these NW precursors by oxidation followed by oxide etching, Si NWs with diameters ranging from 50 nm to above 100 nm are obtained. The pattern of NWs is determined solely by photolithography. Various geometries ranging from T-junctions to circular coils are demonstrated in addition to straight NWs along specific crystallographic orientations. The number of NWs in a stack is determined by the number of etch cycles utilized. Due to the precise lithographic definition of NW location and orientation, the technique provides a convenient batch-compatible tool for the integration of NWs with MEMS. This aspect is demonstrated with a microgripper, where an electrostatic actuation mechanism is simultaneously fabricated with the accompanying NW endeffectors. Mechanical integrity of the NW–MEMS bond and the manipulation capability of the gripper are demonstrated. Overall, the proposed technique exhibits a batch-compatible approach to the issue of micronanointegration