Rocco Crescenzi

MEMS-Based Conjugate Surfaces Flexure Hinge

This paper presents a new concept flexure hinge for MEMS applications and reveals how to design, construct, and experimentally test. This hinge combines a curved beam, as a flexible element, and a pair of conjugate surfaces, whose contact depends on load conditions. The geometry is conceived in such a way that minimum stress conditions are maintained within the flexible beam. A comparison of the new design with the other kind of revolute and flexible joints is presented. Then, the static behavior of the hinge is analyzed by means of a theoretical approach, based on continuum mechanics, and the results are compared to those obtained by means of finite element analysis (FEA) simulation. A silicon hinge prototype is also presented and the construction process, based on single step lithography and reactive ion etching (RIE) technology, is discussed. Finally, a crucial in–SEM experiment is performed and the experimental results are interpreted through the theoretical models.

Development of Micro-Grippers for Tissue and Cell Manipulation with Direct Morphological Comparison

Although tissue and cell manipulation nowadays is a common task in biomedical analysis, there are still many different ways to accomplish it, most of which are still not sufficiently general, inexpensive, accurate, efficient or effective. Several problems arise both for in vivo or in vitro analysis, such as the maximum overall size of the device and the gripper jaws (like in minimally-invasive open biopsy) or very limited manipulating capability, degrees of freedom or dexterity (like in tissues or cell-handling operations). This paper presents a new approach to tissue and cell manipulation, which employs a conceptually new conjugate surfaces flexure hinge (CSFH) silicon MEMS-based technology micro-gripper that solves most of the above-mentioned problems. The article describes all of the phases of the development, including topology conception, structural design, simulation, construction, actuation testing and in vitro observation. The latter phase deals with the assessment of the function capability, which consists of taking a series of in vitro images by optical microscopy. They offer a direct morphological comparison between the gripper and a variety of tissues.

The development of a MEMS/NEMS-based 3 D.O.F. compliant micro robot

Microrobots are used nowadays in several fields of application, specially in mini invasive surgery. However, they are rather difficult to be constructed, and the traditional micro machining tools are not adequate yet to built the smaller parts. The construction of the microrobots is even harder if more than one D.O.F. are required for the mechanism, because these systems are more complicated. This paper deals with the development of a 3 D.O.F. planar micro platform with remote system of actuation. The new approach of design and manufacturing is based on two innovative solutions: a) the adoption of the technologies used to built MEMS, Micro Electro Mechanical Systems; b) the introduction of new flexural hinge to develop compliant micro mechanisms. The new concept of flexural hinge is described in the paper, also from a theoretical point of view. Several example of possible structures are proposed and analyzed, together with their remote wire actuation systems. Finite Element Analysis (FEA) has been also adopted to analyze the system performance under small deformations. The principle of fabrication is, then, described. The process consists of a sequence of single steps which have allowed to achieved an overall maximum size down to 3–4 mm and the minimum thickness of the smaller components down to 50µm.

Design, optimization and construction of MEMS-based micro grippers for cell manipulation

The need of micromanipulation devices has been growing rapidly during the last decades, specially in the fields of Biology and Micro-Assembly, and many solutions have been proposed to cope with the increasing demand. The present paper suggests a possible way to micromanipulating objects in various conditions, adopting MEMS technologies to develop a microgripper based on a new flexural hinge, recently patented by the Authors. The micromechanism has been modified considering results obtained through FEA. Finally, a brief description of the construction process is provided, together with some experimental activities.

A Simple Application of Conjugate Profile Theory to the Development of a Silicon Micro Tribometer

Although a certain amount of work has been presented in literature which concerns micro and nano tribology, few contributions have been dedicated to the development of experimental set up for friction assessment in MEMS. The present paper offers a contribution which attempts to fill this gap: the proposal of a new concept design of a micro-tribometer for testing silicon-silicon sliding in MEMS devices, particularly in those obtained via D-RIE process. Since the general contact conditions at the macro scale are very different from those which characterize MEMS, the proposed tribometer is very different from the classic pin-on-disk or block-on-ring. For this reason, a dedicated MEMS has been built, whose only purpose is recreating silicon-silicon sliding under prescribed loads and, then, assessing friction and wear. Since most of MEMS have planar relative motion, the tribometer presented in this article is able study only planar relative motions, and so it has been essentially based on a the creation of a pair of conjugate profiles, whose relative motion has been obtained by using Finite Element Analysis (FEA) simulations, rather than by the classical centrodes theory.Copyright

New selective wet processing

A new selective processing technique based on a confined dynamic liquid drop\meniscus is presented. This approach is represented by the localized wet treatment of silicon wafers using dynamic liquid drop that while is in contact with the wafer forms a dynamic liquid meniscus. The main scientific innovation and relevance introduced by this work have been applied to industrial solar cell production and on silicon wafer metal bumps formation for the IC interconnection (i.e. copper pillars). Such new technique allows to touch in specific defined positions the silicon wafer in order to perform any kind of wet processing (e.g. etching, cleaning and/or plating) without the need of any protective resist. To investigate on pendant dynamic liquid drops and dynamic liquid meniscus use of computational fluid dynamic technique (i.e. numerical techniques to accurately predict fluid flows) was followed and is presented. An experimental setup has been built to validate the calculations. Numerical results showed a good agreement with experimental ones. Prototypes heads, using stereo-lithography systems, were developed and localized selective plating without the need of lithography step was performed on silicon.

Transfer layer technology for the packaging of high power modules

Most power electronic modules are specifically designed for the customer and this entails intense labour during the production phase. The monolithic integration for power electronic devices in the form of power IC has not proven to be efficient, neither from a technical, nor from an economic point of view. In a typical high power module the power devices are assembled on a heatsink and, driver, sensor and protection circuits are mounted on separate PCBs assembled to the power devices. This results in low performance and high cost. Higher integrated power modules are produced assembling power devices in die format onto a DCB (Direct Copper Bonding) substrate and interconnect them by wire bonding technique [1]. The relative driver, sensor and protection circuits are surface mounted on a separate PCB assembled with the former.

Technology and design of innovative flexible electrode for biomedical applications

The electrochemotherapy is an effective treatment that requires the application of an intense electric field to the tumoral tissue to open the cellular membrane and deliver drugs. This work will present the results of the ongoing research project, showing a new technology and design geometry that allows to realize flexible electrodes able to wrap biological tissues bringing the necessary electric field intensity for the electroporation of cells to reach a unique penetration depth to the centimeter range. The flexible electrode is realized by conversion of porous silicon into nano-porous metals (copper and/or gold) filled by a biocompatible thermoplastic polymer.

A novel micromachined loudspeaker topology

A novel topology for a micromachined acoustic speaker suitable for cellular phones is proposed in this paper. The membrane is composed of two materials, each of them with different function: a silicon moving part acting as a rigid piston, and polymer annulus acting only as suspension. The high ratio between Young moduli and masses of membrane and suspension leads to a simpler design of the mass-spring-damper system. This new topology can be obtained thanks to a new micromachining technology, that leads to an higher adhesion between polymer and silicon. Simulations presenting the main micro-loudspeaker parameters (e.g. SPL, frequency response) are presented in details as also the principal technological steps.

High uniformity and high speed copper pillar plating technique

In this work we report the application of the selective wet processing technique based on dynamic liquid meniscus for copper pillar bumps (CPB) plating. The industrial plating of copper for CPB process is typically carried out at 2 μm/min. A much higher copper deposition rate is necessary to improve throughput for this process. To achieve higher deposition rates of copper the hydrodynamic issue that is natural for all conventional plating baths processes must be solved. A number of solutions is proposed towards realization of high speed and high throughput CPB plating process. Uniformity of copper pillar over a 6-inches silicon wafer is presented and the morphology and shapes of pillars are investigated by scanning electron microscopy (SEM). Copper pillar height and dimension are investigated within different topology over the wafer showing the robustness of the process for the thickness uniformity. Preliminary investigation of the CPB plating shows the uniformity of better than 2 % within 6” silicon wafer.