Gino Rinaldi

Quantitative Boundary Support Characterization for Cantilever MEMS

Microfabrication limitations are of concern especially for suspended Micro-Electro-Mechanical-Systems (MEMS) microstructures such as cantilevers. The static and dynamic qualities of such microscale devices are directly related to the invariant and variant properties of the microsystem. Among the invariant properties, microfabrication limitations can be quantified only after the fabrication of the device through testing. However, MEMS are batch fabricated in large numbers where individual testing is neither possible nor cost effective. Hence, a suitable test algorithm needs to be developed where the test results obtained for a few devices can be applied to the whole fabrication batch, and also to the foundry process in general. In this regard, this paper proposes a method to test MEMS cantilevers under variant electro-thermal influences in order to quantify the effective boundary support condition obtained for a foundry process. A non-contact optical sensing approach is employed for the dynamic testing. The Rayleigh-Ritz energy method using boundary characteristic orthogonal polynomials is employed for the modeling and theoretical analysis.

A polyimide based resistive humidity sensor

Purpose – To establish an accurate and sensitive method to characterize the moisture content of a particular environment.Design/methodology/approach – This paper proposes a relatively simple humidity sensor design consisting of electrodes on a suitable substrate coated with a polyimide material. The changes in relative humidity are denoted by a corresponding change in the polyimide materials electrical resistance profile. The design proposed in this work can be microfabricated and integrated with electronic circuitry. This sensor can be fabricated on alumina or silicon substrates. The electrode material can be made up of nickel, gold or aluminum and the thickness of the electrodes ranges typically between 0.2 and 0.3 μm. The sensor consists of an active sensing layer on top of a set of electrodes. The design of the electrodes can be configured for both resistive and capacitive sensing.Findings – The polyimide materials ohmic resistance changes significantly with humidity variations. Changes in resistanc...

An improved method for predicting microfabrication influence in atomic force microscopy performances

This paper presents the application of the concept of boundary conditioning to the prediction of spring constant of atomic force microscope (AFM) cantilevers after considering the inherent microfabrication limitations. The boundary support conditions of micromechanical structures such as AFM probes are non-classical in nature, and they influence the modal response and natural frequencies of the cantilever that cannot be modelled on purely classical boundary conditions. In this paper, an AFM cantilever end support is modelled with artificial translational and rotational springs in order to capture the deviation from classical boundary conditions. The dynamic and static behaviour of the beam is investigated by the Rayleigh-Ritz energy method using boundary characteristic orthogonal polynomials and compared with published theoretical and experimental results. The comparison shows a close agreement and presents an insight into the inherent limitation associated with AFM probe fabrication processes that would affect the stiffness of the probe.

Boundary characterization of microstructures through thermo-mechanical testing

A variety of silicon foundry processes available for microsystem implementation are available at the present time. The manufacturing methods and the associated process tolerances employed at a particular foundry will determine the performance of the finished devices. Moreover, micro-electro-mechanical systems (MEMS) often require processes that are difficult to control. Device-to-device variations can occur even in batch microfabricated systems. One particular limitation of MEMS foundry processes, in general, is associated with non-classical boundary support conditions due to over/under etching of silicon. These non-classical support conditions will affect the static and dynamic performance of the microsystem. This condition has important implications in atomic force microscopy applications where the targeted natural frequencies are given a wide tolerance due in large part to microfabrication limitations. This paper presents the boundary characterization of single crystal silicon microcantilevers through thermo-mechanical testing. A non-contact optical sensing approach is used for the experimentation. The Rayleigh–Ritz energy method incorporating boundary characteristic orthogonal polynomials is used for the prediction analysis.

Tuning the dynamic behaviour of cantilever MEMS based sensors and actuators

Purpose – This paper seeks to establish an analytical reference model in order to optimize the frequency response of MEMS cantilever structures using cutouts.Design/methodology/approach – Presented in this work is a method to tune the frequency response of MEMS cantilevers by using single cutouts of various sizes. From an interpretation of the analytical results, mass and stiffness domains are defined as a function of the cutout position on the cantilever. In this regard, the elastic properties of the MEMS cantilever can be trimmed through mechanical tuning by a single cutout incorporated into the device geometry. The Rayleigh‐Ritz energy method is used for the modeling. Analytical results are compared with FEM and experimental results.Findings – The eigenvalues are dependent on the position and size of the cutout. Hence, the frequency response of the cantilever can be tuned and optimized through this approach.Research limitations/implications – MEMS microsystems are sensitive to microfabrication limitati...

Variable-frequency EPR study of Mn 2þ -doped NH 4 Cl 0:9 I 0:1 single crystal at 9.6, 36, and 249.9 GHz: structural phase transition

Multifrequency electron paramagnetic resonance studies on the Mn(2+) impurity ion in a mixed single crystal NH(4)Cl(0.9)I(0.1) were carried out at 9.62 (X-band) in the range 120-295 K, at 35.87 (Q-band) at 77 and 295 K, and at 249.9 GHz (far-infrared band) at 253 K. The high-field EPR spectra at 249.9 GHz are well into the high-field limit leading to a considerable simplification of the spectra and their interpretation. Three magnetically inequivalent, but physically equivalent, Mn(2+) ions with their respective magnetic Z-axes oriented along the crystallographic [100], [010], [001] axes were observed. Simultaneous fitting of EPR line positions observed at X-, Q-, and far infra-red bands was performed using a least-squares procedure and matrix diagonalization to estimate accurately the Mn(2+) spin-Hamiltonian parameters. The temperature variation of the linewidth and peak-to-peak intensities of the EPR lines indicate the presence of lambda-transitions in the mixed NH(4)Cl(0.9)I(0.1) crystal at 242 and 228 K consistent with those observed in the pure NH(4)Cl and NH(4)I crystals, respectively. A superposition-model analysis of the spin-Hamiltonian parameters reveals that the local environment of the Mn(2+) ion is considerably reorganized to produce axially symmetric crystal fields about the respective Z-axes of the three magnetically inequivalent ions as a consequence of the vacancy created due to charge-compensation when the divalent Mn(2+) ion substitutes for a monovalent NH(4)(+) ion in the NH(4)Cl(0.9)I(0.1) crystal. This reorganization is almost the same as that observed in NH(4)Cl and NH(4)I single crystals, although the latter two are characterized by different, simple cubic and face-centered cubic, structures.

Experimental investigation on the dynamics of MEMS structures

Modeling, manipulating and testing of the dynamic performances of micro-electro-mechanical systems (MEMS) devices are very important in building successful microsystems. However, MEMS devices pose several significant difficulties in characterization. The physical dimensions of MEMS devices are such that conventional measurement and characterization techniques cannot be used since the sensor would interfere with the measurement. Hence, non-contact sensing systems offer many advantages for MEMS characterization. One important issue in characterizing and troubleshooting MEMS devices is the differentiation between electrical and mechanical effects. By definition, MEMS devices are comprised of electrical and mechanical components forming integrated electro-mechanical systems. The dynamic response of these devices is often difficult to determine because of the coupled electro-mechanical behavior. It is also known that the dynamic response is influenced by the limitation of fabrication processes and the material conditions. Hence, this paper proposes a simpler method to verify the dynamic behavior of MEMS structures using Laser Doppler Velocimeter (LDV). Non-contact vibration measurements are thus possible with such a testing system that can lead to significant improvements in the accuracy and precision of MEMS testing. The dynamic experiments are conducted on different devices and the test results are compared with prediction.

Dynamic pressure as a measure of gas turbine engine (GTE) performance

Utilizing in situ dynamic pressure measurement is a promising novel approach with applications for both control and condition monitoring of gas turbine-based propulsion systems. The dynamic pressure created by rotating components within the engine presents a unique opportunity for controlling the operation of the engine and for evaluating the condition of a specific component through interpretation of the dynamic pressure signal. Preliminary bench-top experiments are conducted with dc axial fans for measuring fan RPM, blade condition, surge and dynamic temperature variation. Also, a method, based on standing wave physics, is presented for measuring the dynamic temperature simultaneously with the dynamic pressure. These tests are implemented in order to demonstrate the versatility of dynamic pressure-based diagnostics for monitoring several different parameters, and two physical quantities, dynamic pressure and dynamic temperature, with a single sensor. In this work, the development of a dynamic pressure sensor based on micro-electro-mechanical system technology for in situ gas turbine engine condition monitoring is presented. The dynamic pressure sensor performance is evaluated on two different gas turbine engines, one having a fan and the other without.

Simple and versatile micro‐cantilever sensors

Purpose – The purpose of this paper is to demonstrate the simplicity and versatility of micro‐cantilever based sensors and to present the influence of added mass and stress on the frequency response of the sensor in order to determine the most suitable sensing domain for a given application.Design/methodology/approach – The frequency response of micro‐cantilevers depends not only on the applied mass and surface stress, but also on the mass position. An interpretation of the theoretical frequency results of the 1st and 2nd natural frequencies, for added mass, identifies a nodal point for the 2nd natural frequency which demonstrates mass invariance. Hence, at this nodal point, the frequency response remains constant regardless of mass and may be used for identifying purely induced surface stress influences on the micro‐cantilevers dynamic response. The Rayleigh‐Ritz energy method is used for the theoretical analysis. Theoretical results are compared with experimental results.Findings – A graph of the 2nd n...

Dynamic Synthesis of Microsystems Using the Segment Rayleigh–Ritz Method

Microsystem development requires accurate and parametric-based modeling as well as experimental validation of the effects of multiphysics influences such as electrostatic, thermal, and mechanical on microsystems in a systematic manner. This work attempts to synthesize the influence of electrothermomechanical influences on microsystems using an energy-based method, namely, the segment Rayleigh-Ritz (SRR), thereby making it possible to study the multiphysics influences on the dynamic behavior of microsystems in a simplified and unified way. Electrostatic, thermal, and geometrical influences along with microfabrication limitations related to the boundary support are studied on cantilever-based microsystems. Silicon-on-insulator-based technology is used for demonstration purposes. The SRR energy method was developed in order to improve the theoretical formulation for microsystems with nonuniform properties. The method of artificial springs is employed to model the boundary support, electrostatic influences, and intersegmental boundaries. The microfabricated support conditions were quantified through a rotational stiffness, and its invariance with geometry, temperature, and electrostatic field was verified through dynamic testing under electrothermal influences. Comparison with test results validates the dynamic synthesis modeling for microstructures. This approach can be expanded further to nondimensional design optimization and for targeted performance tuning of the static and dynamic behavior of microsystems.