All-photoplastic, soft cantilever cassette probe for scanning force microscopy

Abstract

Multiple single-lever probes for scanning force microscopy arranged in a cassette design and made of a low-stiffness photoplastic material have been developed and successfully tested by imaging DNA molecules. The new concept consists of a column of a one-dimensional array of cantilevers with integrated tips, the first of which is used for imaging and the others are spares in case the first one becomes degraded. When this happens, the lever is mechanically removed from the chip so that the next spare becomes ready for scanning. The probes are fabricated of a photoplastic material, which allows simple batch fabrication and facilitates realization of specific mechanical properties for cantilevers-such as low stiffness-that are very difficult to achieve with classical silicon technology. The batch fabrication process, based on spin coating and subsequent near-ultraviolet exposure and development steps of the photoplastic SU-8, results in well-controlled and uniform mechanical properties of the probes within the same chip, as well as for different chips over a 4 in. wafer. Successful images of soft, condensed-matter samples were taken using these cassette probes, making consecutive readdressing of the same DNA molecule with two different cantilevers possible. Thus, a worn-out cantilever can be replaced by a new fresh one with only small positional adjustments and without any changes in the operating conditions. This ease of operation was provided by the cassette concept and the excellent uniformity of the mechanical cantilever characteristics.

Micromachined Photoplastic Probes for Scanning Probe Microscopy

“…(1) is pushed down to break off the damaged cantilever so that the first spare cantilever can be pushed (2) into the same position as the old one, precisely determined by mechanical alignment structures on cassette and holder. Reprinted with permission from [26], © American Vacuum Society. on the same chip as the front cantilever, which is used to scan the sample.…”

“…More details on the fabrication, characterization and testing of the cantilever cassette probes can be found in Ref. [26].…”

“…(b) Image of the same molecule with the second lever of a cassette with a better tip. Reprinted with permission from[26], © American Vacuum Society.…”

Micromachined High-Aspect-Ratio Parylene Spring and Its Application to Low-Frequency Accelerometers

“…However, very thin beams of 1 in width and 450 in length were required. An alternative approach for producing a soft spring is to use photosensitive polymer materials [2]- [4]. Lee et al [4] employed SU-8 to make a cantilever beam for atomic force microscopy with a spring constant of 0.248 N/m.…”

UV-LIGA: From Development to Commercialization

“…Scanning probes for AFM (atomic force microscopy) or SNOM (scanning near-field optical microscopy) are good examples of possible applications brought by this photoplastic material [9]. Figure 2 shows an example where a complete cassette consisting of five different probes with pre-defined cut-off zones is entirely fabricated in SU-8 [10]. SU-8-based technology has established itself as an intermediate solution between the low-cost, high-volume fabrication provided by injection molding and the fine, controlled feature characteristics given by silicon technologies.…”