Piezoresistive Membrane Surface Stress Sensors for Characterization of Breath Samples of Head and Neck Cancer Patients

For many diseases, where a particular organ is affected, chemical by-products can be found in the patient’s exhaled breath. Breath analysis is often done using gas chromatography and mass spectrometry, but interpretation of results is difficult and time-consuming. We performed characterization of patients’ exhaled breath samples by an electronic nose technique based on an array of nanomechanical membrane sensors. Each membrane is coated with a different thin polymer layer. By pumping the exhaled breath into a measurement chamber, volatile organic compounds present in patients’ breath diffuse into the polymer layers and deform the membranes by changes in surface stress. The bending of the membranes is measured piezoresistively and the signals are converted into voltages. The sensor deflection pattern allows one to characterize the condition of the patient. In a clinical pilot study, we investigated breath samples from head and neck cancer patients and healthy control persons. Evaluation using principal component analysis (PCA) allowed a clear distinction between the two groups. As head and neck cancer can be completely removed by surgery, the breath of cured patients was investigated after surgery again and the results were similar to those of the healthy control group, indicating that surgery was successful

Scanning probe with tuning fork sensor, microfabricated silicon cantilever and conductive tip for microscopy at cryogenic temperature

A quartz tuning-fork (TF)-based scanning probe is presented for local electrical transport measurements on quantum devices below the liquid 4 He temperature. The TF is utilized to drive and sense the mechanical oscillation of an attached, microfabricated cantilever featuring a conductive tip made of platinum silicide. The microfabricated structure allows the application of an external voltage to the tip, while the cantilever is electrically grounded. The probe was characterized at room temperature, 70 K, and 2 K. It was found that spatial sensitivity decreased with temperature. Imaging a gold surface at 2 K was successfully performed. A number of probes can be batch-fabricated, thus shortening the lead time for conducting experiments in cryogenic scanning force microscopy

Micro- and nanosystems for biology and medicine

The development of new tools and instruments for biomedical applications based on nano- (NEMS) or microelectromechanical systems technology (MEMS) are bridging the gap between the macro- and the nano-world. The well mastered microtechnique allows controlling many parameters of these instruments, which is essential for conducting reproducible and repeatable experiments in the life sciences. Examples are multifunctional scanning probe sensors for cell biology, an arthroscopic scanning force microscope for minimally invasive medical interventions and a nanopore sensor for single molecule experiments in biochemistry. This paper reviews some of the activities conducted in a fruitful interdisciplinary collaboration between physicists, engineers, biologists and physicians

Sic high temperature pressure transducer

The invention concerns a pressure transducer comprising a deflecting membrane, said membrane comprising two piezoresistors (10, 11) of different types, said piezoresistors being arranged such that a same stress or a same strain is applied on said piezoresistors and said piezoresistors (10, 11) yield changes in resistance, wherein a piezoresistor of a first type (10) is positioned such that its current direction is perpendicular to the stress direction (trans verse) and a piezoresistor of a second type is parallel to the stress direction (longitudinal), allowing, when a tensile stress is applied to the transducer, said piezoresistor of the first type to increase its resistance and said piezoresistor of the second type to decrease the resistance; or when a compressive stress is applied to the transducer, said piezoresistor of the first type to decrease its resistance and said piezoresistor of the second type to increase the resistance; wherein said piezoresistor of the first type (10) has a specific width and a length as short as possible and said piezoresistor (11) of the second type has a width as short as possible and a length as long as possible

Dynamic behavior of the tuning fork AFM probe

We recently introduced a new self-actuating and self-sensing atomic force microscope (AFM) probe based on a quartz tuning fork and a micro-fabricated cantilever. This system has two degrees of freedom, associated with its two components. We developed a model for describing how the sample-tip interaction is transduced to the tuning fork. It is based on two coupled spring-mass systems. In a first step, the coupling between the tuning fork and the cantilever was investigated to reveal the influential factors. The analysis of these factors enabled us to deduce their effect on the whole system and to optimize the sensitivity of this novel probe. The theoretical analysis was compared with experimental results and it was found that the model appropriately describes the probe in a qualitative manner while further refinement will be needed for achieving a correct quantitative description

Piezoresistive n-Type 4H-SiC Pressure Sensor with Membrane Formed by Mechanical Milling

A 4H-SiC pressure sensor with piezoresistive transducers, for harsh environment applications, e.g., high temperature (~650°C) and/or in corrosive chemicals is presented. The sensing membrane, 1 mm in diameter and 50 µm in thickness, was formed by milling (drilling) a bulk single crystal SiC wafer. Both transverse and longitudinal piezoresistors were formed on the membrane out of an n-type SiC epitaxial layer. Ohmic contacts were obtained with Ta/Ni/Pt metallization followed by annealing at 1000°C for 20 min. The sensor was assembled on a small board and characterized under hydrostatic pressures up to 60 bar at room temperature. The obtained pressure sensitivity was 268 µV/V/bar. The sensor chip was exposed in air at 600°C for 165 hours and changes in bridge resistance were measured

Platinum TSVs for High-Temperature Processing and Operation of Microsystems

We report on the fabrication and characterization of high-temperature Pt-TSVs. A LPCVD silicon nitride passivation layer was implemented to protect the TSVs from oxidation during high-temperature treatments and wet HF-based post-processing steps, the later being widely used for the release of MEMS mechanical structures. An ohmic contact between the TSV metallization and a silicon device layer was created and maintained, during and after high-temperature treatments. These “via first” TSVs were able to withstand post-processing temperatures up to 850 °C; the specific contact resistance was investigated. Moreover, they are of interest for high temp- perature applications; they operated stably for at least 24 h at up to 450°C