Piezoresistive cantilever array for life sciences applications

Atomic force microscopy with integrated on-chip interferometric readout

The most common readout technique used in atomic force microscopy (AFM) is based on optical beam deflection (OBD), which relies on monitoring deflection of the cantilever probe by measuring the position of the laser beam reflected from the free end of the AFM cantilever. Although systems using the OBD readout can achieve subnanometre displacement resolution and video rate imaging speeds, its main limitation is size, which is difficult to minimise, thus limiting multiprobe imaging capability. Currently, system miniaturisation has been accommodated by adopting on-chip electrical readout solutions, often at the expense of measurement sensitivity. To date, no cost-effective AFM readout solution exists without sacrificing either measurement sensitivity, system miniaturisation, or multiprobe array scalability. In this paper we present an AFM probe with integrated on-chip optical interferometric readout based on silicon photonics. Our AFM probe combines the advantages of subnanometre resolution of optical readouts with on-chip miniaturisation. The adopted approach determines deflection of the cantilever using an integrated on-chip photonics waveguide by monitoring the separation between the sensing cantilever and an interrogating grating. The implemented methodology provides ultimate interferometric resolution and sensitivity, on-chip miniaturisation, and array scalability, which makes possible ultrafast multiprobe-array AFM imaging. Using a Digital Instruments D3000 AFM retrofitted with our cantilever probe and integrated readout, we report sub-nanometre AFM topography images obtained on reference samples. We demonstrate RMS static AFM noise level of 19 pm, outperforming the operation of this system in its standard, optical beam deflection configuration (51 pm). The noise spectrum measurements of our probe indicate that the integrated readout is shot noise limited, achieving a deflection noise density (DND) of 36fm/Hz.

Tip-Based Nanofabrication for Scalable Manufacturing

Tip-based nanofabrication (TBN) is a family of emerging nanofabrication techniques that use a nanometer scale tip to fabricate nanostructures. In this review, we first introduce the history of the TBN and the technology development. We then briefly review various TBN techniques that use different physical or chemical mechanisms to fabricate features and discuss some of the state-of-the-art techniques. Subsequently, we focus on those TBN methods that have demonstrated potential to scale up the manufacturing throughput. Finally, we discuss several research directions that are essential for making TBN a scalable nano-manufacturing technology.

Parallel nanoimaging and nanolithography using a heated microcantilever array

We report parallel topographic imaging and nanolithography using heated microcantilever arrays integrated into a commercial atomic force microscope (AFM). The array has five AFM cantilevers, each of which has an internal resistive heater. The temperatures of the cantilever heaters can be monitored and controlled independently and in parallel. We perform parallel AFM imaging of a region of size 550 μm × 90 μm, where the cantilever heat flow signals provide a measure of the nanometer-scale substrate topography. At a cantilever scan speed of 1134 μm s(-1), we acquire a 3.1 million-pixel image in 62 s with noise-limited vertical resolution of 0.6 nm and pixels of size 351 nm × 45 nm. At a scan speed of 4030 μm s(-1) we acquire a 26.4 million pixel image in 124 s with vertical resolution of 5.4 nm and pixels of size 44 nm × 43 nm. Finally, we demonstrate parallel nanolithography with the cantilever array, including iterations of measure-write-measure nanofabrication, with each cantilever operating independently.

Parallel AFM imaging and force spectroscopy using two-dimensional probe arrays for applications in cell biology

Atomic force microscopy (AFM) investigations of living cells provide new information in both biology and medicine. However, slow cell dynamics and the need for statistically significant sample sizes mean that data collection can be an extremely lengthy process. We address this problem by parallelizing AFM experiments using a two-dimensional cantilever array, instead of a single cantilever. We have developed an instrument able to operate a two-dimensional cantilever array, to perform topographical and mechanical investigations in both air and liquid. Deflection readout for all cantilevers of the probe array is performed in parallel and online by interferometry. Probe arrays were microfabricated in silicon nitride. Proof-of-concept has been demonstrated by analyzing the topography of hard surfaces and fixed cells in parallel, and by performing parallel force spectroscopy on living cells. These results open new research opportunities in cell biology by measuring the adhesion and elastic properties of a large number of cells. Both properties are essential parameters for research in metastatic cancer development.

Sub-ppm detection of vapors using piezoresistive microcantilever array sensors

The performance of microfabricated piezoresistive cantilever array sensors has been evaluated using various vapors of volatile organic compounds including alkanes with different chain length from 5 (n-pentane) to 14 (n-tetradecane). We demonstrate that piezoresistive microcantilever array sensors have the selectivity of discriminating individual alkanes in a homologous series as well as common volatile organic compounds according to principal component analysis. We developed a new method to evaluate the sensitivity, taking advantage of the low vapor pressures of alkanes with longer chains, such as n-dodecane, n-tridecane and n-tetradecane, under saturated vapor conditions. This method reveals sub-ppm sensitivity and the cantilever response is found to follow the mass of evaporated analytes as calculated using a quantitative model based on the Langmuir evaporation model.

Review: Semiconductor Piezoresistance for Microsystems

Piezoresistive sensors are among the earliest micromachined silicon devices. The need for smaller, less expensive, higher performance sensors helped drive early micromachining technology, a precursor to microsystems or microelectromechanical systems (MEMS). The effect of stress on doped silicon and germanium has been known since the work of Smith at Bell Laboratories in 1954. Since then, researchers have extensively reported on microscale, piezoresistive strain gauges, pressure sensors, accelerometers, and cantilever force/displacement sensors, including many commercially successful devices. In this paper, we review the history of piezoresistance, its physics and related fabrication techniques. We also discuss electrical noise in piezoresistors, device examples and design considerations, and alternative materials. This paper provides a comprehensive overview of integrated piezoresistor technology with an introduction to the physics of piezoresistivity, process and material selection and design guidance useful to researchers and device engineers.