A. Tonin

Assessment of insulated conductive cantilevers for biology and electrochemistry

This paper describes the characterization and application of electrically insulated conductive tips mounted on a cantilever for use in an atomic force microscope and operated in liquid. These multifunctional probes were microfabricated and designed for measurements on biological samples in buffer solution, but they can also be employed for electrochemical applications, in particular scanning electrochemical microscopy. The silicon nitride based cantilevers had a spring constant ≤0.1 N m-1 and a conductive tip, which was insulated except at the apex. The conductive core of the tip consisted of a metal, e.g. platinum silicide, and exhibited a typical radius of 15 nm. The mechanical and electrical characterization of the probe is presented and discussed. First measurements on the hexagonally packed intermediate layer of Deinococcus radiodurans demonstrated the possibility to adjust the image contrast by applying a voltage between a support and the conductive tip and to measure variations of less than 1 pA in faradaic current with a lateral resolution of 7.8 nm.

Integrated atomic force microscopy array probe with metal–oxide–semiconductor field effect transistor stress sensor, thermal bimorph actuator, and on-chip complementary metal–oxide–semiconductor electronics

A microfabricated 2×1 array of active and self-detecting cantilevers is presented for applications in atomic force microscopy (AFM). The integrated deflection sensor is based on a stress sensing metal–oxide–semiconductor transistor. Full custom complementary metal–oxide–semiconductor amplifiers for signal readout are combined on the same chip. A sensor sensitivity of 2.25 mV/nm, or a change in current ΔId/Id=2.8×10−6/nm, was obtained at the final output stage. Three Al–Si thermal bimorph actuators are integrated on each cantilever for self-excitation and feedback actuation. The efficiencies of the heaters are 2.4–4.7 K/mW. In the experimental setup, a maximum displacement of 8 μm was achieved at 45 mW input. A pair of parallel AFM images in the constant height mode, a typical tapping mode image, and a constant force image with 1.3 μm high features have been successfully taken with the array probe.

Development of Insulated Conductive Probes with Platinum Silicide Tips for Atomic Force Microscopy in Cell Biology

A microfabrication process of a multifunctional probe is introduced for atomic force microscopy and various electrochemical measurements on biological samples in buffer solution. The silicon nitride probes have a spring constant lower than 0.1 N/m and a conductive tip, which is tightly insulated except at the apex. The conductive core of the tip consists of PtxSi y and shows a typical radius of curvature of 15 nm. A simultaneous measurement of topography and electrical current on graphite in air was demonstrated.

Atomic force microscope for planetary applications

We have developed, built and tested an atomic force microscope (AFM) for planetary science applications, in particular for the study of Martian dust and soil. The system consists of a controller board, an electromagnetic scanner and a micro-fabricated sensor-chip. Eight cantilevers with integrated, piezoresistive deflection sensors are aligned in a row and are engaged one after the other to provide redundancy in case of tip or cantilever failure. Silicon and molded diamond tips are used for probing the sample. Images can be recorded in both, static and dynamic operation mode. In the latter case, excitation of the resonance frequencies of the cantilevers is achieved by vibrating the whole chip with a piezoelectric disk.

Characterization of an integrated force sensor based on a MOS transistor for applications in scanning force microscopy

In this article an integrated force sensor based on a stress-sensing MOS transistor is introduced for applications in scanning force microscopy (SFM) . The sensor configuration will be described, and theoretical and experimental investigations of the sensitivity will be presented. With the fabrication process, consisting of a standard CMOS process and post-processing (conventional silicon bulk micromachining), cantilevers with MOS transistors integrated at the base for deflection detection have been fabricated. The cantilevers typically have a spring constant of 1 N m-1, are 400 to 950 um in length and have a mechanical resonance frequency between 6.2 and 35 kHz. It is found that the stress sensitivity of the MOS transistor changes with the gate voltage, while being independent of the drain voltage. The cantilevers have successfully been used for SFM imaging in both contact mode and dynamic mode (tapping mode). These cantilevers together with integrated circuits are expected to be well suited for mass production because of their CMOS processing compatibility.

Parallel scanning AFM with on-chip circuitry in CMOS technology

We present the first force sensors for application in Atomic Force Microscopy (AFM) fabricated with industrial CMOS technology. Sensing is based on two different detection schemes: a piezoresistive Wheatstone bridge and stress-sensing MOS transistors. The system combines on a single chip (i) two cantilevers for parallel scanning, (ii) thermal actuators for independent deflection of the two cantilevers, (iii) sensors to measure the deflection, and (iv) offset compensation and signal conditioning circuitry. The AFM probes were tested in contact and dynamic mode. In the dynamic mode, images with a resolution of better than 20 /spl Aring/ were recorded. Moreover, we successfully took parallel scanning images in contact mode.

On-chip circuitry for a CMOS parallel scanning AFM

We present on-chip signal conditioning circuitry for the first parallel scanning Atomic Force Microscope sensors fabricated in industrial CMOS technology. The system combines, on a single chip, (1) two cantilevers for parallel scanning, (2) thermal actuators for independent deflection of the two cantilevers, (3) sensors to measure the deflection and (4) offset compensation and signal conditioning circuitry. It was fabricated using the 2.0 micrometers CMOS process of Austria Mikro Systeme and CMOS compatible post-processing micromachining. Scanning images were successfully acquired in contact and dynamic mode. The resolution of the recorded tapping mode images is better than 20 angstroms.

Piezoresistive membrane-type surface stress sensor arranged in arrays for cancer diagnosis through breath analysis

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.

Insulated Conductive Probes for in situ Experiments in Structural Biology

We report about the development of a multifunctional AFM probe, which allows to perform simultaneous measurements of topography and electrical properties of biological samples in a buffer solution. The quality of the AFM probes has been experimentally assessed by acquiring topography measurements of bacteriorhodopsin membranes in buffer solution and topographical and electrical current images of HOPG in air.

Development of insulated conductive probes with platinum-silicide tips for AFM in cell biology

In this paper, we report about the development of this multifunctional AFM probe. This insulated conductive probes to measure the topography of biological membranes.