•We fabricated piezoresistive membrane- and cantilever-based surface stress sensors.•The devices were similarly functionalized with dextran and tested as humidity sensors.•Membranes were five times more reproducible compared to cantilevers-based sensors.•Simulations confirmed that the functionalization is key for a good reproducibility.

We present the fabrication, characterization and successful medical application of a membrane-type surface stress sensor (MSS), arranged in arrays for molecular detection in gaseous phase. Made out of SOI substrate, a round membrane with a diameter of 500 μm and a thickness of 2.5 μm is suspended by four sensing beams with integrated p-type piezoresistors, composing a full Wheatstone bridge. The membrane is coated with a thin polymer layer, which reacts with volatile molecules and produces a deflection of the membrane. The membranes were functionalized with various polymers and characterized as humidity sensors with a sensitivity of 87 mV/%RH and a time constant (Tau63%) of 1.3 s. Finally, through breath analysis and the use of principal component analysis (PCA), we were able, in a double blind trial, to distinguish cancer patients and healthy persons.

With their capability for real-time and label-free detection of targets ranging from gases to biological molecules, nanomechanical sensors are expected to contribute to various fields, such as medicine, security, and environmental science. For practical applications, one of the major issues of nanomechanical sensors is the difficulty of coating receptor layers on their surfaces to which target molecules adsorb or react. To have measurable deflection, a single-side coating is commonly applied to cantilever-type geometry, and it requires specific methods or protocols, such as inkjet spotting or gold-thiol chemistry. If we can apply a double-side coating to nanomechanical sensors, it allows almost any kind of coating technique including dip coating methods, making nanomechanical sensors more useful with better user experiences. Here we address the feasibility of the double-side coating on nanomechanical sensors demonstrated by a membrane-type surface stress sensor (MSS) and verify its working principle by both finite element analysis (FEA) and experiments. In addition, simple hand-operated dip coating is demonstrated as a proof of concept, achieving practical receptor layers without any complex instrumentation. Because the double-side coating is compatible with batch protocols such as dip coating, double-side-coated MSS represents a new paradigm of one-chip-one-channel (channels on a chip are all coated with the same receptor layers) shifting from the conventional one-chip-multiple-channel (channels on a chip are coated with different receptor layers) paradigm.

The standard lithographic techniques to fabricate electronic components involve the use of polymers, baking steps and chemicals. This typically restricts their application to flat substrates made up of standard materials. Stencil lithography has been proposed as a stable alternative to the standard lithographic techniques. In this paper, we demonstrate the completely resistless all-through-stencil fabrication of electronic components, by performing all essential fabrication steps—implantation, etching and metallization—using stencil lithography. This is performed on a planar substrate as well as on pre-patterned 3D substrates, thus showing the potential of this technique for applications in the field of accelerometers, pressure, gas and radiation sensors.

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.

We present a new generation of piezoresistive nanomechanical Membrane-type Surface stress Sensor (MSS) chips, which consist of a two dimensional array of MSS on a single chip. The implementation of several optimization techniques in the design and microfabrication improved the piezoresistive sensitivity by 3~4 times compared to the first generation MSS chip, resulting in a sensitivity about ~100 times better than a standard cantilever-type sensor and a few times better than optical read-out methods in terms of experimental signal-to-noise ratio. Since the integrated piezoresistive read-out of the MSS can meet practical requirements, such as compactness and not requiring bulky and expensive peripheral devices, the MSS is a promising transducer for nanomechanical sensing in the rapidly growing application fields in medicine, biology, security, and the environment. Specifically, its system compactness due to the integrated piezoresistive sensing makes the MSS concept attractive for the instruments used in mobile applications. In addition, the MSS can operate in opaque liquids, such as blood, where optical read-out techniques cannot be applied.

Piezoresistive cantilevers have been extensively used for many years as force sensors, mass detectors, image scanning tools, and as biosensors, which have absorbate layers generating surface stress upon reaction with analyte. We will introduce different piezoresistive biosensor designs, e.g., single clamped cantilever and membrane-type sensor. The different sensor structures are compared with respect to DR/R value of a single piezoresistor embedded on the device structures with different arrangements. The quantitative DR/R values of each sensor were calculated with a simulation tool based on finite element analysis, to be introduced as another contribution to this conference. Based on the results, we will present an optimized single clamped cantilever with one piezoresistor and an optimized biosensor structure, which is not a simple “cantilever” rather it consists of an “absorbate membrane” suspended by four “sensing beams”.

We present 2D cantilever arrays for parallel AFM and their fabrication process using a silicon nitride cantilever with molded tip as the base element of the array. They are designed either for (i) force indentation onto living cells and stiffness mapping, or (ii) cell-to-cell adhesion test applications. The former needs the cantilevers with 0.03N/m and the tip radius 50 – 200nm. The latter requires 3N/m and 2500nm, respectively. The technique to fabricate those cantilever arrays with different specifications, without significantly changing the fabrication process, is the core of this work. The parallel AFM system itself has been developed and presented elsewhere (M. Favre, et al., Journal of Molecular Recognition, vol. 24, pp. 446-452, 2011). To obtain cantilevers with different spring constants from a wafer, V-grooves structures along the cantilevers were introduced in the cantilever design. An analytical model and an FEA simulation confirmed that the spring constant can be varied up to two decades by changing the V-groove depth. To obtain a large tip radius required for cell handling, we developed a mold enlarging/rounding step and obtained a tip with a radius up to 4μm.

The use of ion-beam sputtered Al2O3 to passivate the mirrors of semiconductor injection lasers is described. Dense films, which offer considerable protection against corrosion, can be deposited without damage to the crystal surface. The overall quality of the passivation is demonstrated by long-term stress testing of the lasers.

Biosensors often require detecting infinitesimal amount of species, thus their readout must be improved for highest sensitivity and best Signal-to-Noise ratio. We will present a simulation tool for piezoresistive strain sensors, which takes into account nonuniform current flow in e.g., a U-shaped piezoresistor, and calculates local resistivity changes based on the piezoresistive coefficients with corresponding directions. This simulation tool yields DR/R as a result. Thus a real piezoresistor layout, rather than a symbolic resistor, can be simulated. Important aspects of optimum piezoresistive readout for biosensors will be discussed.

In this study, we introduce five unique scanning probes developed in our laboratory for different fields of application. These probes are the results of excellent collaborations with many external partners. Each probe possesses many advanced features that one can hardly obtain with plane probes for conventional optical deflection system. The applications of these probes are very versatile, from atomic force microscope for the exploration of Mars to in vivo measurements of human knee cartilage. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The monolithic or hybrid integration of sensors and actuators (S&A) onto CMOS platforms is of great importance to reduce the device size and cost as well as to facilitate new functionalities and better performance. Hence, S&As on CMOS platforms are important and convincing examples of "more than Moore." This chapter focuses on a broad range of aspects of S&As on CMOS platforms. First, the basic concept is introduced, followed by a detailed description of the fundamentals of current S&A concepts. The current market situation is then described, demonstrating the great opportunities for S&As. A substantial part of the chapter is devoted to the various techniques and fabrication processes for monolithic and hybrid integration of S&As on CMOS. Successful examples of very large-scale integration (VLSI) of S&As on CMOS platforms are also described. Current research into the use nanostructures for new or better S&A functionalities or improved performance is described in an additional subsection. Finally, the equally important back-end-of-the-line aspects in large-volume production, packaging, and testing are presented. The chapter closes with the authors' outlook and view on the challenges and opportunities in research, development, production, and marketing of new and better S&As, VLSI-type S&As on single-chip CMOS platforms, and S&A networks.