Si Cantilever Research Articles

Fabrication of conducting AFM cantilevers with AlN-based piezoelectric actuators

This paper presents a new fabrication technology for conducting AFM cantilevers with integrated AlN-based piezoelectric actuators. A major effort has been done for the process integration of a high quality AlN layer onto the Si cantilever together with a high wear resistance, PtSi-based conducting tip. Functional AFM devices have been successfully tested in tapping mode imaging experiments. Such type of cantilevers are of great interest for dynamic AFM applications especially for tapping or dithering mode AFMs as well as for using the piezoelectric structures as an integrated position sensor.

3-7 圧電薄膜を用いた振動エナジーハーベスターの特性評価(OS3 電池レス・デバイスのためのエネルギーハーベストの展開)

We fabricated piezoelectric vibration energy harvesters composed of PZT and lead-free KNN thin films on Si cantilevers and characterized the output voltage and power of those piezoelectric films. Both of the PZT and KNN films were deposited on Pt-coated Si substrates by rf-magnetron sputtering. The harvesters had a simple unimorph cantilever structure with the almost same dimensions, and the characteristics of power generation were examined. When we applied the acceleration of 10m/s^2 on the PZT and KNN energy harvesters, they generated the output power of 1.11 and 1.01μW at the resonant frequency under 10m/s^2, indicating lead-free KNN films are comparable to PZT films for the performance for power generation.

Development of Micro Tensile Testing Method in an FIB System for Evaluating Grain Boundary Strength

A micro tensile testing method for evaluating grain boundary strength was developed. Specimens of 2 � 2 � 10 mm having one grain boundary were made by focused ion beam (FIB) micro-processing and tensioned in an FIB system. The load was measured from the deflection of the Si cantilever and the displacement was also monitored in situ. The method was applied to aged and unaged Fe-Mn-P alloy specimens with different grain boundary P segregation. The load at intergranular fracture decreased with increasing P segregation. [doi:10.2320/matertrans.M2010320]

MEMS based humidity sensor using Si cantilever beam for harsh environmental conditions

Sensing and controlling of humidity is a major issue in various industries. Many of the equipments in industries require monitoring and controlling humidity for its efficient and reliable operation. This paper presents the design, fabrication and complete characterization of a micro cantilever based humidity sensor for harsh environmental conditions. A Si cantilever humidity sensor based on capacitive principle is designed and displacement analysis is performed on the sensor. The polyimide, acts as a sensing material for this sensor. The polyimide is coated over the beam to sense the humidity. If the humidity absorbed by the polyimide material increases, the mass of the beam is also increased. The deflection of the beam causes the change in capacitance. The relative humidity can be calculated using the change in capacitance. The beam had an appreciable deflection causing a notable change in capacitance. The variation of capacitance is in the order of picofarads. The sensor is designed in a structure that can tolerate the harsh environmental conditions like pressure, temperature, etc.

On the calibration of rectangular atomic force microscope cantilevers modified by particle attachment and lamination

A simple but effective method for estimating the spring constant of commercially available atomic force microscope (AFM) cantilevers is presented, based on estimating the cantilever thickness from knowledge of its length, width, resonant frequency and the presence or absence of an added mass, such as a colloid probe at the cantilever apex, or a thin film of deposited material. The spring constant of the cantilever can then be estimated using standard equations for cantilever beams. The results are compared to spring constant calibration measurements performed using reference cantilevers. Additionally, the effect of the deposition of Cr and Ti thin films onto rectangular Si cantilevers is investigated.

Nanodiamond-coated silicon cantilever array for chemical sensing

Diamond offers attractive properties as a material for microelectromechanical chemical sensors but is difficult to process in comparison with silicon. Here a method for attaching detonation-derived nanodiamonds to prefabricated and mounted Si cantilever devices is described. It is shown that this hybrid device has a resonant frequency shifted down, compared to Si alone, by around 10% due to a higher spring constant. Exposure to 2,4-dinitrotoluene leads to an easily observed decrease in resonant frequency. The mechanisms behind these observations are discussed and the promise for this form of hybrid cantilever structure for chemical sensors applications highlighted.

Nanoscale Displacements Detected by Evanescent Optical Coupling from an Optical Fiber to a Si Cantilever

Nanoscale Displacements Detected by Evanescent Optical Coupling from an Optical Fiber to a Si Cantilever

Non-Core–Shell Nanostructure Deposition on Focused-Ion-Beam Chemical Vapor Deposition

Nano- and microstructures fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) have a core–shell structure caused by the scattering profiles of Ga ions and secondary electrons (SEs). This structural characteristic makes it difficult to design functions of nano-electromechanical devices. Therefore, non-core–shell structure deposition by the control of SE emission was examined to facilitate the function design of nanoelectromechanical devices. Non-core–shell structure deposition was achieved by applying voltage during carbon nanostructure growth. We also evaluated the growth characteristics of non-core–shell structure deposition. We found that the growth rate of a nanostructure did not change when voltage was applied. Furthermore, we evaluated the mechanical material characteristics (density and Young's modulus) of a non-core–shell structure by measuring of the resonant frequency shift of a Si cantilever using the electron beam method. We found that the non-core–shell structure had a high density (6.5 g/cm3) and a high Young's modulus (800 GPa). These results indicate that the technique for non-core–shell structure deposition is useful in achieving nanoelectromechanical devices.

Functional Microscopy Tip Fabrication by an Electric Conductive Nanowire

The functional microscopy tip was fabricated by an electric conductive nanowire (NW). Single crystalline nickel silicide (NiSi) NW grown by plasma-enhanced chemical vapor deposition has an excellent electrical conductivity. On behalf of the advantages in tiny size and conductivity of NiSi NW, it was utilized as a nanoscale probe. Dielectrophoretic method was applied to position the NW. The NiSi NW containing solution was dropped in an ac electric field applying system to align the NiSi NW on a Si cantilever. The fabricated NiSi NW-sitting functional microscopy tip obtained the information of topography and electrical signals from a nanoscale structure. It shows the high potential of nanoscale microscopy tip fabrication at reduced processing steps.

Simultaneous atomic force and scanning tunneling microscopy study of the Ge(111)-c(2×8) surface

In this article, the authors present the simultaneous noncontact atomic force microscopy and scanning tunneling microscopy measurement of the Ge(111)-c(2×8) surface using PtIr-coated Si cantilevers at room temperature. In both frequency shift and time-averaged tunneling current images at constant-height mode, each atom was clearly resolved. The image contrasts differ because the time-averaged tunneling current image is more directly coupled with local density of states than the frequency shift image. They demonstrate the measurement of the site-specific scanning tunneling spectroscopy (STS) spectra, which are in good agreement with typical STS measurements. Moreover, they demonstrate the simultaneous measurements of site-specific frequency shift and tunneling current as a function of tip-sample distance curves. On the Ge(111)-c(2×8) surface, tunneling current dropped at the near-contact region where a strong tip-sample interaction force is observed.

Micromachining of a newly designed AFM probe integrated with hollow microneedle for cellular function analysis

In order to realize cellular function analysis in a single living cell, we have been developing a newly designed probe for atomic force microscope (AFM), named bioprobe. The proposed bioprobe has a conventional sharp tip superseded by a hollow silicon dioxide microneedle connecting the root to a fluidic microchannel embedded into a silicon (Si) cantilever beam structure. The probe will be capable not only of performing AFM measurements but also of introducing desired biomolecules (DNA, proteins, etc.) into living cells and extracting biomolecules expressed in the cells. In this paper, we describe the most important techniques for fabricating microneedles with a sharpened tip. Then, in order to give mechanical strength enough to be used as AFM probes, a simple fabrication process for structuring Si microstructure close to the base of a needle was proposed. By employing the developed techniques, the prototype bioprobes were successfully fabricated. It was also demonstrated the fabricated probe proved capable of taking AFM images.

Study of GaN epilayers growth on freestanding Si cantilevers

Abstract Five-micron thick freestanding Si cantilevers were fabricated on bulk Si (1 1 1) substrates with surface/bulk micromachining (SBM) process. Then 1-μm thick GaN layers were deposited on the Si cantilevers by metal-organic chemical vapor deposition (MOCVD). Epilayers on cantilever areas were obtained crack-free, and the photoluminescence (PL) spectra verified the stress reduction and better material quality in these suspended parts of GaN. Back sides of the cantilevers were also covered with GaN layers, which prevented the composite beams from bending dramatically. This paper had proved the feasibility of integrating high-quality GaN epilayers with Si micromechanical structures to realize GaN-based micro electro-mechanical system (MEMS).

Use of self-actuating and self-sensing cantilevers for imaging biological samples influid

In this paper, we present a detailed investigation into the suitability of atomic forcemicroscopy (AFM) cantilevers with integrated deflection sensor and micro-actuator forimaging of soft biological samples in fluid. The Si cantilevers are actuated using amicro-heater at the bottom end of the cantilever. Sensing is achieved through p-dopedresistors connected in a Wheatstone bridge. We investigated the influence of the water onthe cantilever dynamics, the actuation and the sensing mechanisms, as well as the crosstalkbetween sensing and actuation. Successful imaging of yeast cells in water using theintegrated sensor and actuator shows the potential of the combination of this actuation andsensing method. This constitutes a major step towards the automation and miniaturizationrequired to establish AFM in routine biomedical diagnostics and in vivo applications.

Damaged Layer Analysis for AFM-Based Mechanical Modifications on (100) Si Surface

Micro/Nanofabrication of silicon substrate based on the atomic force microscope (AFM) followed by wet chemical etching was demonstrated. A specially designed cantilever with a diamond tip, allowing the formation of damaged layer on silicon substrate by a simple scratching process, has been applied instead of conventional Si or Si3N4-based micro cantilever for scanning. A thin damaged layer forms in the substrate at the diamond tip-sample junction along scanning path of the tip, which was found to be a low crystallized amorphous silicon layer. Hence these sequential processes, called tribo nanolithography, TNL, can fabricate 2D or 3D micro structures in nanometer range. The developed TNL tools show outstanding machinability against single crystal silicon wafer. Hence, they are expected to have a possibility for industrial applications as a micro-to-nano machining tool. According to our results, it has been clearly known that the damaged layer withstands against aqueous potassium hydroxide solution, while it dissolves in diluted hydro fluoric (DHF) solution.

Measurement of non-DLVO force on a silicon substrate coated with ammonium poly(acrylic acid) using scanning probe microscopy

The repulsive force originating from steric hindrance of polymers in aqueous solvent was investigated using scanning probe microscopy (SPM). The contact angle (CA) of ammonium poly(acrylic acid) (PAA) solution on the Si surface was measured to estimate the state of the Si substrate. Results of CA measurement show that the Si surface was fully covered with PAA at 0.1 mass% in aqueous solution. The interaction force between the Si tip and the wafer was estimated using the SPM force curve mode. The force curve measured in the ion-exchanged purified water showed the typical relation predicted by Derjaguin–Landau–Verway–Overbeek (DLVO) theory. However, the force curve shape in the 0.1 mass% PAA solution was significantly different. Only a repulsive force was observed at less than about 4 nm of separation distance between the Si wafer and cantilever tip. This distance originated from the steric repulsions of PAA adsorbed onto the Si wafer and cantilever tip.

Fabrication and characterization of all-thin-film magnetoelectric sensors

ac magnetic field sensors based on thin-film magnetoelectric (ME) devices operating at room temperature have been fabricated. The ME layers consist of a sol-gel derived Pb(Zr0.52Ti0.48)O3 film and a sputter deposited Fe0.7Ga0.3 film on Si cantilevers. The ME coupling is substantially improved by depositing a Pt layer at the interface. The ME coefficient up to 1.81 V/Oe cm is obtained at the mechanical resonant frequency of 333 Hz and at dc bias magnetic field of 90 Oe. Clear reduction in the substrate clamping effect is observed as the Si cantilever thickness is systematically reduced down to 35 μm.

The influence of a Si cantilever tip with/without tungsten coating on noncontact atomicforce microscopy imaging of a Ge(001) surface

A sharp probe tip with atomic scale stability is essential and desirable for noncontactatomic force microscopy (NC-AFM) studies at the atomic scale. We observed a Ge(001)surface using both a Si cantilever and a tungsten coated Si cantilever at roomtemperature in order to investigate the influence of the tip apex structure on theNC-AFM images. By using the Si cantilever, we first obtained four types of image atthe atomic scale which can be explained assuming a dimer structure on the tipapex. On the other hand, the home-made tungsten coated tip, which has atomicscale stability and high electric conductivity, imaged the so-called ordered c(4 × 2) structure without any artifacts. The tungsten coated cantilever was found to havesignificantly higher performance for NC-AFM studies at the atomic scale than the Sicantilever.

Simultaneous measurement of force and tunneling current at room temperature

We have performed simultaneous scanning tunneling microscopy and atomic force microscopy measurements in the dynamic mode using metal-coated Si cantilevers at room temperature. Frequency shift (Δf) and time-average tunneling current (⟨It⟩) images are obtained by tip scanning on the Si(111)-(7×7) surface at constant height mode. By measuring site-specific Δf(⟨It⟩) versus tip-surface distance curves, we derive the force (tunneling current) at the closest separation between the sample surface and the oscillating tip. We observe the drop in the tunneling current due to the chemical interaction between the tip apex atom and the surface adatom, which was found recently, and estimate the value of the chemical bonding force. Scanning tunneling spectroscopy using the same tip shows that the tip is metallic enough to measure local density of states of electrons on the surface.

Wafer-scale production of carbon nanofiber probes

The 4in. wafer-scale production of probes tipped with single carbon nanofibers (CNF probes) for scanning probe microscope was achieved by an Ar+-ion-irradiation method. For the wafer-scale production, an arrangement of commercial-type Si cantilevers (tetrahedral Si tips), onto which single CNFs are grown, was optimized to contain 288 cantilevers in a 4in. wafer. The ion-induced CNFs were then batch grown in the wafer scale. Scanning electron microscope observation of 50 of 288 probes randomly selected revealed that the CNFs were linear shaped, ∼400nm in average length and ∼9nm in average radius, and that ∼80% of the probes batch grown were suitable for practical use as qualified probes. Atomic force microscope image of a densely distributed plastic nanocolumn array obtained by the batch-grown CNF probe was clearer and less distorted, compared to that attained by a conventional Si probe. Thus, the ion-irradiation method opened up new route for the wafer-scale production of CNF probes for practical daily use.

Application of ion-induced carbon nanocomposite fibers to magnetic force microscope probes

Small-scale batch fabrication of Co-included carbon nanofibers (Co-CNFs) onto commercially available Si cantilevers for scanning probe microscope by an Ar+-ion-irradiation method with a simultaneous Co supply was demonstrated (eight chips/batch). As confirmed by scanning and transmission electron microscopes equipped with energy dispersive x-ray spectroscopy, Co-CNFs were fibrous and contained Co and C. With increasing the Co supply rate, Co-CNFs decreased in length from ∼600to∼400nm, whereas their diameter was almost independent of the Co supply rate, 20–30nm. As proven by magnetic force microscope (MFM) measurements using the Co-CNF probes, they were applicable as MFM probes. Since various metals including alloys can be incorporated into CNFs, this ion-irradiation method with a simultaneous metal supply was believed to be quite promising for the functionalization of CNF probes for a variety of applications.