Marc A. F. van den Boogaart

Complex oxide nanostructures by pulsed laser deposition through nanostencils

We achieved parallel nanoscale patterning of ferroelectric complex oxides by pulsed laser deposition through a nanostencil (i.e., through a pattern of apertures in a thin free-standing membrane). Ordered arrays of nanostructured barium titanate (BaTiO3) were obtained onto different substrates in a single deposition step, at room temperature, replicating accurately the aperture patterns in the stencil membrane. After a postdeposition annealing treatment, x-ray diffraction pattern showed a nanocrystalline BaTiO3 structure close to the perovskite cubic phase with grains 30–35nm in size. Their local ferroelectric properties were detected using piezoresponse force microscopy.

Nanomechanical Mass Sensor for Spatially Resolved Ultrasensitive Monitoring of Deposition Rates in Stencil Lithography

Keywords: mass sensors ; nanoelectromechanical systems ; nanolithography ; nanomechanical sensors ; High-Frequency Applications ; Cmos-Mems ; Devices Reference LMIS1-ARTICLE-2009-006doi:10.1002/smll.200990007View record in Web of Science Record created on 2009-01-28, modified on 2017-05-10

Fabrication of metallic patterns by microstencil lithography on polymer surfaces suitable as microelectrodes in integrated microfluidic systems

Microstencil lithography, i.e. local deposition of micrometer scale patterns through small shadow masks, is a promising method for metal micropattern definition on polymer substrates that cannot be structured using organic-solvent-based photoresist technology. We propose to apply microstencil lithography to fabricate microelectrodes on flat and 3D polymer substrates, such as PMMA or SU-8, which form parts of microfluidic systems with integrated microelectrodes. Microstencil lithography is accompanied by two main issues when considered for application as a low-cost, reproducible alternative to standard photolithography on polymer substrates. In this paper we assess in detail (i) the reduction of aperture size (clogging) after several metal evaporation steps and corresponding change of deposited pattern size and (ii) loss in the resolution (blurring) of the deposited microstructures when there is a several micrometers large gap between the stencil membrane and the substrate. The clogging of stencil apertures induced by titanium and copper evaporation was checked after each evaporation step, and it was determined that approximately 50% of the thickness of the evaporated metals was deposited on the side walls of the stencil apertures. The influence of a gap on the deposited structures was analyzed by using 18 um thick SU-8 spacers placed between the microstencil and the substrate. The presence of an 18 um gapmade the deposited structures notably blurred. The blurring mechanism of deposited structures is discussed based on a simplified geometrical model. The results obtained in this paper allow assessing the feasibility of using stencil-based lithography for unconventional surface patterning, which shows the limits of the proposed method, but also provides a guideline on a possible implementation for combined polymer-electrode microsystems, where standard photoresist technology fails.

Dynamic stencil lithography on full wafer scale

In this paper, the authors present a breakthrough extension of the stencil lithography tool and method. In the standard stencil lithography static mode, material is deposited through apertures in a membrane (stencil) on a substrate which is clamped to the stencil. In the novel dynamic mode, the stencil is repositioned with respect to the substrate inside the vacuum chamber and its motion is synchronized with the material deposition. This can be done either in a step-and-repeat or in a continuous mode. The authors present the first results proving the accurate x-y-z in situ positioning and movement of our stages during and in between patterning.

Reverse transfer of nanostencil patterns using intermediate sacrificial layer and lift-off process

We propose a new process by which patterns produced by nanostencil lithography can be reversed, so that the final pattern on the substrate has the same contrast (filled or empty) as that of the stencil. In this process, the stencil pattern is first formed on an intermediate sacrificial layer, and then transferred onto the underlying substrate in a reverse manner. Using this process, we can form various pattern structures that cannot be produced by the normal stencil process, such as an array of pores or multiple parallel bridges. Because a bridge in the stencil is transferred also as a bridge on the substrate, we can not only avoid the widening of a narrow bridge pattern by the stress-induced bending of the membrane, but also reduce the width of the bridge even further using the pattern blurring. Using SiO2 as an intermediate layer, we have fabricated various reversed Cr patterns on Si, including an array of 800nm circular pores and a 100-nm-wide and 150-nm-long nanobridge.

Nanomechanical mass sensor for monitoring deposition rates through confined apertures

A nanoelectromechanical mass sensor is used to characterize material deposition rates in stencil lithography. The material flux through micron size apertures is mapped with high spatial (below 1 µm) and deposition rate (below 10 µm/s) resolutions by displacing stencil apertures above the sensor. The sensor is based on a resonating metallic beam with submicron-size width and thickness. The beam is monolithically integrated with a CMOS readout and amplifier circuit to constitute a self-oscillator.

Nanomechanical test structure for optimal alignment in stencil-based lithography

A nanoelectromechanical mass sensor based on a submicron size resonating metallic beam is used to characterize material deposition rates in stencil lithography. The material flux through micron size apertures is mapped with high spatial (below 1 ¿m) and deposition rate (below 10 pm/s) resolutions by displacing stencil apertures above the sensor. It is discussed how the sensor can be used as a test alignment for multi-level nanostencil lithography.