Parallel optical readout of a cantilever array in dynamic mode

In this work we present parallel optical readout of a cantilever array which operates in dynamic mode using a standard optical beam deflection configuration containing only one laser-detector pair. We show accurate readout of the resonance frequency shift of an individual cantilever within an array by designing arrays where each cantilever has a different resonance frequency. The different resonance frequencies are created by giving each cantilever a different length and allow parallel readout of all cantilevers within the array. We show that even if the cantilevers are closely spaced each cantilever resonance frequency can be individually tracked without signs of cross-talk at current measurement precision (below 12 mHz). Interference of the laser light reflecting of each cantilever is observed when the amplitude of the cantilever is on the order of the wavelength of the laser light

Microfabricated photoplastic cantilever with integrated photoplastic/carbon based piezoresistive strain sensor

L. Gammelgaard, P. A. Rasmussen, M. Calleja, P. Vettiger, and A. Boisen Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark We present an SU-8 micrometer sized cantilever strain sensor with an integrated piezoresistor made of a conductive composite of SU-8 polymer and carbon black particles. The composite has been developed using ultrasonic mixing. Cleanroom processing of the polymer composite has been investigated and it has been shown that it is possible to pattern the composite by standard UV photolithography. The composite material has been integrated into an SU-8 microcantilever and the polymer composite has been demonstrated to be piezoresistive with gauge factors around 15–20. Since SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, this polymer based strain sensor is more sensitive than a similar silicon based cantilever sensor.Peer reviewe

Monte Carlo transient phonons transport in silicon and germanium at nanoscales

Heat transport at nanoscales in semiconductors is investigated with a statistical method. The Boltzmann Transport Equation (BTE) which characterize phonons motion and interaction within the crystal lattice has been simulated with a Monte Carlo technique. Our model takes into account media frequency properties through the dispersion curves for longitudinal and transverse acoustic branches. The BTE collisional term involving phonons scattering processes is simulated with the Relaxation Times Approximation theory. A new distribution function accounting for the collisional processes has been developed in order to respect energy conservation during phonons scattering events. This non deterministic approach provides satisfactory results in what concerns phonons transport in both ballistic and diffusion regimes. The simulation code has been tested with silicon and germanium thin films; temperature propagation within samples is presented and compared to analytical solutions (in the diffusion regime). The two materials bulk thermal conductivity is retrieved for temperature ranging between 100 K and 500 K. Heat transfer within a plane wall with a large thermal gradient (250 K-500 K) is proposed in order to expose the model ability to simulate conductivity thermal dependence on heat exchange at nanoscales. Finally, size effects and validity of heat conduction law are investigated for several slab thicknesses

Atomic Scale Memory at a Silicon Surface

The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of 5 atom rows. The writing process involves removal of Si atoms with the tip of a scanning tunneling microscope. The memory can be reformatted by controlled deposition of silicon. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.Comment: 13 pages, 5 figures, accepted by Nanotechnolog

High-aspect-ratio, ultrathick, negative-tone near-UV photoresist and its applications for MEMS

Detailed investigations of the limits of a new negative-tone near-UV resist (IBM SU-8) have been performed. SU-8 is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications. We have demonstrated that with single-layer coatings, thicknesses of more than 500 km can be achieved reproducibly. Thicker resist layers can be made by applying multiple coatings, and we have achieved exposures in 1200 IJ-m thick, double-coated SU-8 resist layers. We have found that the aspect ratio for near-UV (400 nm) exposed and developed structures can be greater than 18 and remains constant in the thickness range between 80 and 1200 IJ-m. Vertical sidewall profiles result in good dimensional control over the entire resist thickness. To our knowledge, this is the highest aspect ratio reported for near-UV exposures and the given range of resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. The application potential of SU-8 is demonstrated by several examples of devices and structures fabricated by electroplating and photoplastic techniques. The latter is especially interesting as SU-8 has attractive mechanical properties

Low-cost PDMS seal ring for single-side wet etching of MEMS structures

We describe a new O-ring setup for wet-etching processes of microelectromechanical systems (MEMS) . Our new low-cost approach using siloxane-based seal rings entails the single-side etching of silicon and silicon dioxide using potassium hydroxide and buffered hydrofluoric acid, respectively. With this approach, the wafer is not immersed into the etching solution, but only the side to be etched is in contact with the solution, hence the previously fabricated device elements on the other side of the wafer are not damaged. In one process for etching silicon the etch solution is heated by an infrared lamp. We describe the fabrication of various cantilever-based sensors, such as arrays of 0.8-um thick levers for a chemical/electronic nose, and 5-um-thick silicon cantilevers having piezoresistive sensors. Our technique has gooduniformity and process control and, in addition, eliminates mechanical stress on the fragile wafers incurred by wafer chucks, which are required for the conventional immersion approach. It has improved process yield and reduces the waste of chemicals

Piezoresistive cantilever designed for torque magnetometry

New piezoresistive silicon cantilevers designed specifically for torque magnetometry on microscopic samples have been microfabricated and tested. These levers have been optimized to detect the torque in two directions corresponding to flexion and torsion. Torque resolution of 10 E-14 N m can be achieved depending on the operating mode. In one version an integrated loop allows an absolute calibration of the device with an accuracy of ~1%. This loop can also be used to excite the lever mechanically. One application is the determination of the mass of nanogram samples by measuring the resonance frequency shift (nanobalance)

Heat transfer between a nano-tip and a surface

We study quasi-ballistic heat transfer through air between a hot nanometer-scale tip and a sample. The hot tip/surface configuration is widely used to perform nonintrusive confined heating. Using a Monte-Carlo simulation, we find that the thermal conductance reaches 0.8 MW.m-2K-1 on the surface under the tip and show the shape of the heat flux density distribution (nanometer-scale thermal spot). These results show that a surface can be efficiently heated locally without contact. The temporal resolution of the heat transfer is a few tens of picoseconds.Comment: 4 page

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by Dip Pen Nanolithography

We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting a multi-instrument and multi-technique local detection and analysis. Moreover the smooth surface of the Au squares (abput 5-10 angstrom roughness) allows to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label free detection methods for DNA nanoarrays based on the use of scanning probes.Comment: Langmuir (accepted