Fabrication Of Cantilevers Research Articles

A Novel SU8 Polymer Anchored Low Temperature HWCVD Nitride Polysilicon Piezoresitive Cantilever

In this paper, we present a novel approach for fabricating piezoresistive silicon nitride cantilevers using polymer as an anchor. In our approach, the silicon nitride structural layers, as well as the polycrystalline silicon piezoresistive layer, are deposited by a low temperature hot-wire chemical vapor deposition process. The novelty of this process is that the silicon wafer is not consumed and is reusable, and the process also allows use of alternate materials for cantilever fabrication in place of silicon substrate. The fabricated silicon nitride cantilevers are characterized for their mechanical and electromechanical behavior.

Critical assessment of the determination of residual stress profiles in thin films by means of the ion beam layer removal method

Residual stresses and their distribution within individual layers are a general concern in thin film technology. Here we use a recently developed ion beam layer removal method to determine the stress profile in a thin film system. The system consists of a thin tungsten and titanium nitride film deposited on a silicon substrate. The stresses are calculated from the deflection of a focused ion beam machined cantilever by means of Euler–Bernoulli beam theory and finite element simulations coupled with optimizing algorithms, and the results of the two methods are critically compared. Case studies taking into account manufacturing related variations in the cantilever geometry, different boundary conditions and relaxation during cantilever fabrication are performed. We find that the stress distribution in the thin film system is strongly influenced by the boundary conditions and the cantilever fabrication, while manufacturing related variations in the cantilever geometry only slightly influence the stress distribution.

Piezoresistive cantilever working in a shear force mode for in situ characterization of exposed micro- and nanostructures

This paper presents a method of characterization micro- and nanostructures defined in a photolithography process. To implement this method a measurement system composed of an atomic force microscope (AFM) integrated with a system for maskless lithography was developed. This integration enables exposed patterns to be examined in situ, without any necessity for a developing process. The microscope works in a shear force mode, uses a cantilever with a piezoresistive method of detecting deflection and can be used for measuring surfaces with high aspect ratio by applying an appropriate technology of sharpening in a focused ion beam process. The cantilever fabrication process, its calibration and examination procedures are presented. Finally, the AFM images of structures scanned directly after exposure are shown.

Process Control of Cantilever Deflection for Sensor Application Based on Optical Waveguides

This paper reports on the fabrication of cantilever silicon-on-insulator (SOI) optical waveguides and presents solutions to the challenges of using a very thin 260-nm active silicon layer in the SOI structure to enable single-transverse-mode operation of the waveguide with minimal optical transmission losses. In particular, to ameliorate the anchor effect caused by the mean stress difference between the active silicon layer and buried oxide layer, a cantilever flattening process based on Ar plasma treatment is developed and presented. Vertical deflections of 0.5 μm for 70-μm-long cantilevers are mitigated to within few nanometers. Experimental investigations of cantilever mechanical resonance characteristics confirm the absence of significant detrimental side effects. Optical and mechanical modeling is extensively used to supplement experimental observations. This approach can satisfy the requirements for on-chip simultaneous readout of many integrated cantilever sensors in which the displacement or resonant frequency changes induced by analyte absorption are measured using an optical-waveguide-based division multiplexed system.

Fabrication and testing of polymer cantilevers for VOC sensors

We investigated the size and mode dependencies of the resonance frequencies and quality factors of PMMA (polymethyl methacrylate) and PC (polycarbonate) cantilevers under atmospheric pressure in order to obtain fundamental data for polymer-based VOC (volatile organic compound) sensors. PMMA cantilevers and PC cantilevers are fabricated by hot embossing, bonding, and polishing techniques. Variations in the vibration mode result in large variations in the resonance frequencies and quality factors of these cantilevers. The measured resonance frequencies correlated well with the theoretical undamped resonance frequency of a flexural-vibrating cantilever. The measured quality factors varied from 10 to more than 100, depending on the vibration mode. A higher mode tended to exhibit a higher quality factor.

Process-induced stress and hydrogen effects on monolithic integrated BiCMOS-MEMS resonators

In this article, the simultaneous fabrication of MEMS and Bi-CMOS components on a monolithic integrated micro-cantilever resonator is investigated. Surface micromachining method for cantilever fabrication has been merged with conventional CMOS process, and release of MEMS structure is conducted after CMOS process. We for the first time propose the additive effects of hydrogen and MEMS steps induced mechanical stress on the IC performance, and at the same time provide a re-adjusting method for integrated process design, in which the NMOS/PMOS threshold voltage is re-adjusted to symmetry by utilizing the MEMS-process-induced IC performance degradation. On-chip digital/analog Bi-CMOS circuits function properly as demonstrated. The proposed re-adjustment process, suitable for fabrications with a variety of design CMOS-MEMS integrated process flexibilities, has the potential to fabricate integrated devices (high quality factor variable capacitors, micromirror arrays and multi-axis gyroscopes etc.).

Note: Micro-cantilevers with AlN actuators and PtSi tips for multi-frequency atomic force microscopy

We report the design, fabrication, and characterization of cantilevers with integrated AlN actuators and conductive PtSi tips for multi-frequency atomic force microscopy. These cantilevers also possess a stepped-rectangular geometry. The excellent dynamic behavior of these cantilevers is investigated using both finite-element simulations and experimental methods. Several imaging experiments are presented to illustrate the efficacy and versatility of these cantilevers.

Fabrication of cantilever with self-sharpening nano-silicon-tip for AFM applications

A simple, high yield method for the fabrication of cantilever with nano-silicon-tip by wet etching for atomic force microscopy (AFM) applications is described in this paper. The nano-silicon-tips with well controlled dimensions are fabricated by self-sharpening anisotropic wet etching technologies using a special pentagon etch mask design. The spring constant of the cantilever according to demand can be easily realized by changing the design of the etch mask and tuning the etching time in the fabrication process. A fabrication yield as high as 90 % has been realized for the AFM probes on 2 inch wafers. The height of tips on the cantilever is 10–15 μm, and the apex of each nano-silicon-tip typically has a radius of curvature of 5–10 nm. The cantilever’s spring constant can be well controlled within the range of 0.8–120 N m−1. The fabricated AFM probes are capable of generating high quality AFM image comparable with the commercial probes available in our lab.

Epitaxial Growth, Mechanical, Electrical Properties of SiC/Si and SiC/Poli-Si

We have investigated 3C-SiC layers grown on silicon and on poli-Si in order to realize test MEMS structures. The strain of the films were investigated by the fabrication of cantilevers, beams, springs and we successfully fabricated a Double-Ended-Tuning-Fork double clamped SiC resonator on the film, with perfectly aligned actuation electrode.

Two-dimensional cantilever array with varying spring constants and tip radii for life-science applications

A fabrication process for realising two-dimensional cantilever arrays for parallel force spectroscopy of biological samples is presented. The parallel optical atomic force microscopy readout system has been developed and presented elsewhere. The arrays are designed either for (i) force-indentation onto living cells to obtain stiffness mapping or (ii) cell adhesion experiments. Both experiments require very different spring constants and tip radii of curvature. The arrays are based on silicon nitride cantilevers with molded tips. The fabrication process includes an advanced molding process and a thermocompression bonding of two silicon wafers. V-groove structures along the cantilevers, which increase the area moment of inertia, were introduced in the cantilever design. This feature enables the fabrication of cantilevers with different spring constants but same footprint from one wafer. An analytical model and experimental results confirmed that the spring constant of the cantilever (200 x 50 x 0.45 mu m) could be increased up to two decades (0.03-5 N/m) by changing the depth of the V-grooves. To realise the large tip radius required for cell adhesion experiments, an enlarging/rounding procedure has been applied to a truncated pyramidal tip mold. With this process, the authors obtained tips with a radius up to 4 mu m.

Fabrication and characterization of an attonewton-sensitivity Si cantilever with an Nb micro-ring

We have fabricated ultrasensitive silicon cantilevers integrated with a superconducting Nb microring as a key part of a flux quantum-based force measurement system and have characterized both their mechanical and superconducting properties by using mechanical methods. A 50-nm-thick Nb ring with inner and outer radii of 5 µm and 10 µm was mounted by DC magnetron sputtering and lift-off on the end of a 410-µm-long, 4-µm-wide and 340-nm-thick single-crystalline silicon cantilever. The cantilever showed a force sensitivity as good as \({{4.2 aN} \mathord{\left/ {\vphantom {{4.2 aN} {\sqrt {Hz} }}} \right. \kern-\nulldelimiterspace} {\sqrt {Hz} }}\) at 3 K, which was estimated from its spring constant of 2.6 × 10−5 N/m and a quality factor of 31000. The superconducting property of the Nb micro-ring was observed from the variation of the cantilever’s vibration amplitude while the vibration was driven by an excitation coil, showing a transition temperature of 7 K. The superconducting transition was also confirmed through an electrical transport measurement for a separately-prepared Nb strip film on a silicon wafer.

Fabrication and Testing of Polymer Cantilevers for VOC Sensor

Abstract The mode dependences of resonance frequencies and quality factors in a PMMA (polymethyl methacrylate) cantilever and a PC (Polycarbonate) cantilever at atmospheric pressure are investigated to obtain fundamental data for polymer-based VOC (volatile organic compounds) sensors. The PMMA cantilever and the PC cantilever are fabricated using hot embossing, bonding and polishing techniques. The resonance frequencies and the quality factors are found to vary largely depending on the vibration mode. The measured resonance frequencies correlate well with the theory of undamped resonance frequency of a flexural-vibrating cantilever. The measured quality factors varied from less than 20 to more than 100 depending on the vibration mode. A higher mode tended to exhibit a higher quality factor. The highest quality factor of 100 was obtained on the 4th flexural mode in both the PMMA and PC cantilever.

Process-Induced Stress and Hydrogen Effects on Monolithic Integrated CMOS-MEMS Micro-Bimaterial Cantilever Sensor Array

Abstract A monolithic integrated bimaterial micro-cantilever resonant infrared sensor with on-chip auxiliary circuits was fabricated and tested. Surface micromachining method for cantilever fabrication has been merged with conventional CMOS process, and release of MEMS structure is conducted after CMOS process. Both the Cr/Au felling off the polysilicon cantilever during releasing process and the performance degradation of MOSFETs manufactured by standard CMOS or post-CMOS process are ascribed to the additive effects of hydrogen and mechanical stress. A novel post-CMOS process was raised to decrease the mechanical stress and to retain the metal layer of Cr/Au. On-chip digital/analog Bi-CMOS circuits function properly as demonstrated.

Electrical properties of BaTiO3 based ferroelectric capacitors grown on oxide sacrificial layers for micro-cantilevers applications

An investigation of all oxide ferroelectric capacitors based on SrRuO3/BaTiO3/SrRuO3 multi-layers grown on sacrificial oxide layers of YBa2Cu3O7 and MgO for Micro-Electro-Mechanical systems applications is reported. By insertion of additional MgO or SrTiO3 buffer layers the orientation of the BaTiO3 film can be controlled allowing the fabrication of suspended cantilevers using the 31 and the 33 piezoelectric modes. The electrical properties of SrRuO3/BaTiO3/SrRuO3 capacitors are changed compared with those grown directly on a single crystal substrate by the introduction of sacrificial layers. Circuit modeling of the electrical characteristics of these devices shows that a reduction of the deposition pressure for BaTiO3 produces a decrease of the parasitic shunting conductance (modeled with a resistor in parallel to the capacitance of the device) which reduces the resistive losses present in the BaTiO3 film. However for extremely low deposition pressure the quality of the polarization hysteresis loops is compromised.Particulates present on the surface of the YBa2Cu3O7 increase the parasitic conductance at low frequency in the capacitive structure grown on this sacrificial layer. Good electrical properties are obtained for the capacitive structures grown on top of the MgO sacrificial layers at pressures equal or lower than 8Pa.

Design and Fabrication of a PZT Cantilever for Low Frequency Vibration Energy Harvesting

In this study, a PZT cantilever with a Si proof mass is designed and fabricated for a low frequency energy harvesting application. A mathematical model of a multi-layer composite beam was derived and applied in a parametric analysis of the piezoelectric cantilever. Finally, the dimensions of the cantilever were determined for the resonant frequency of the cantilever. Our cantilever design was based on MATLAB and ANSYS simulations. For this simulation, the proof mass volumes were varied from 0 to 0.5 mm3 and resonant frequencies were calculated from 833.5 Hz to 125.5 Hz, respectively. Based on simulation, we fabricated a device with beam dimensions of about 4.10 mm x 0.48 mm x 0.012 mm, and an integrated Si proof mass with dimensions of about 0.481 mm x 0.48 mm x 0.45 mm. The resonant frequency, maximum peak voltage, and highest average power of the cantilever device were 224.8 Hz, 4.8 mV, and 2.24 nW, respectively.

Pattern buried oxide in silicon-on-insulator-based fabrication of floppy single-crystal-silicon cantilevers

For the purpose of high-yield fabrication of single-crystal-silicon cantilevers based on a silicon-on-insulator (SOI) wafer, the internal compressive stress effect of the BOX has been investigated. The large stress in the BOX is responsible for the BOX cracking at the end of the bulk etching. For the cantilevers with comparable thickness with the BOX in the authors' experiments, the cantilevers break with the BOX cracking, which leads to the failure or low yield of the fabrication. Patterning the BOX has been proposed to release the stress and avoid the cantilever breaking. The yield based on this method is as high as 100', and the cantilevers show high quality factor and force sensitivity in vacuum measurements. Patterning the BOX effectually ensures the high-yield fabrication of cantilevers, especially meaningful for the floppy cantilevers. The method proposed here is also promising for the high-yield fabrication of other floppy sensors based on a SOI wafer.

Fabrication of biopolymer cantilevers using nanoimprint lithography

The biodegradable polymer poly(l-lactide) (PLLA) was introduced for the fabrication of micromechanical devices. For this purpose, thin biopolymer films with thickness around 10μm were spin-coated on silicon substrates. Patterning of microcantilevers is achieved by nanoimprint lithography. A major challenge was the high adhesion between PLLA and silicon stamp. Optimized stamp fabrication and the deposition of a 125nm thick fluorocarbon anti-stiction coating on the PLLA allowed the fabrication of biopolymer cantilevers. Resonance frequency measurements were used to estimate the Young’s modulus of the device material.

Stress-driven AlN cantilever-based flow sensor for fish lateral line system

In this work, we report on the fabrication and characterization of stress-driven aluminum nitride (AlN) cantilevers to be applied as flow sensor for fish lateral line system. The fabricated structures exploit a multilayered cantilever AlN/molybdenum (Mo) and a Nichrome 80/20 alloy as piezoresistor. Cantilever arrays are realized by using conventional micromachining techniques involving optical lithography and etching processes. The fabrication of the piezoresistive cantilevers is reported and the operation of the cantilever as flow sensor has been investigated by electrical measurement under nitrogen flowing condition showing a sensitivity to directionality and to low value applied forces.

Fabrication of resonant micro cantilevers with integrated transparent fluidic channel

Microfabricated cantilevers are proving their potential as excellent tools for analysis applications. In this paper, we describe the design, fabrication and testing of resonant micro cantilevers with integrated transparent fluidic channels. The cantilevers have been devised to measure the density of fluids or detect particles suspended in a fluid by sensing the change in total mass of the structure. The 4×4μm2 integrated microfluidic channel makes it possible to flow a fluid through the channel while the cantilevers are resonating. The movement of any particles (present in the fluid) can be visually observed through the transparent fluidic channel. The resonant frequency of the cantilever is changed by the fluid inside the channel, due to the change in mass. The shift in the resonant frequency can be translated into a density of the fluid or into the presence of macro/micro molecules. Such cantilevers can be used as density sensors, to monitor growth of biological cells, measure mass of particles, etc.

Design and Fabrication of Piezoresistive Based Encapsulated Poly-Si Cantilevers for Bio/chemical Sensing

Cantilever-based sensing is a growing research field not only within micro regime but also in nano technology. The technology offers a method for rapid, on-line and in-situ monitoring of specific bio/chemical substances by detecting the nanomechanical responses of a cantilever sensor. Cantilever with piezoresistive based detection scheme is more attractive because of its electronics compatibility. Majority of commercially available micromachined piezoresistive sensors are bulk micromachined devices and are fabricated using single crystal silicon wafers. As substrate properties are not important in surface micromachining, the expensive silicon wafers can be replaced by cheaper substrates, such as poly-silicon, glass or plastic. Here we have designed SU-8 based bio/chemical compatible micro electro mechanical device that includes an encapsulated polysilicon piezoresistor for bio/chemical sensing. In this paper we report the design, fabrication and analysis of the encapsulated poly-Si cantilevers. Design and theoretical analysis are carried out using Finite Element Analysis software. For fabrication of poly-silicon piezoresistive cantilevers we followed the surface micromachining process steps. Preliminary characterization of the cantilevers is presented.