Jens Bonitz

Synthesized femtosecond laser pulse source for two-wavelength contouring with simultaneously recorded digital holograms

A dual-wavelength femtosecond laser pulse source and its application for digital holographic single-shot contouring are presented. The synthesized laser source combines sub-picosecond time scales with a wide reconstruction range. A center wavelength distance of the two separated pulses of only 15 nm with a high contrast was demonstrated by spectral shaping of the 50 nm broad seed spectrum centered at 800 nm. Owing to the resulting synthetic wavelength, the scan depth range without phase ambiguity is extended to the 100-microm-range. Single-shot dual-wavelength imaging is achieved by using two CMOS cameras in a Twyman-Green interferometer, which is extended by a polarization encoding sequence to separate the holograms. The principle of the method is revealed, and experimental results concerning a single axis scanner mirror operating at a resonance frequency of 0.5 kHz are presented. Within the synthetic wavelength, the phase difference information of the object was unambiguously retrieved and the 3D-shape calculated. To the best of our knowledge, this is the first time that single-shot two-wavelength contouring on a sub-ps time scale is reported.

CVD TiN layers as diffusion barrier films on porous SiO 2 aerogel

In this work the compatibility of MOCVD TiN barrier films on porous SiO2 aerogel as low-k dielectric was investigated. The continuity, roughness, and sheet resistance, Rs, of the barrier as well as the electrical properties of the aerogel were investigated. A continuous TiN barrier on uncapped and PECVD SiN capped aerogel exists at 30 and ≤20 nm, respectively. The high surface roughness of the TiN is caused by the aerogel layer. TiN penetration into uncapped aerogel was detected in the interface region, whereas capped low-k material shows no interaction with the barrier film.

Wafer level approaches for the integration of carbon nanotubes in electronic and sensor applications

In this work we give an overview about recent developments in the integration technology of CNTs. We focus on wafer level approaches with the CVD and DEP method for growing as well as depositing CNTs in a defined way. So that we present methods to manipulate CNT growth structure, growth mode as well as growth inhibition in thermal CVD processes. This is highlighted by a unique growth structure opening new possibilities for CNT integration. Likewise, we show recent developments in scaling up the DEP method on wafer level. We round it up with the fabrication of CNT vias and MEMS structures containing CNT sensor elements.

Deformation Measurements of High-Speed MEMS With Combined Two-Wavelength Single-Pulse Digital Holography and Single Phase Reconstruction Using Subpicosecond Pulses

Holographic contouring of high-speed microelectromechanical system optical scanner mirrors operating at resonance frequencies close to 1 kHz is performed with ultrashort-pulse lasers containing two spectral components. These particular pulses are obtained by shaping the spectrum of sub-30 fs pulses of a Ti:sapphire laser system by an acousto-optic programmable dispersive filter. The separation of the two spectral components is adjustable within the 50-nm gain bandwidth. Single-pulse dual-wavelength contouring is achieved by an extended Twyman-Green type interferometer including two CMOS cameras. The deformation obtained from a single-wavelength interferogram is combined with the coarse-shape information deduced from the phase difference map of the two interferograms captured at different wavelengths to yield a combined reconstruction.

Wafer-level technology for integration of carbon nanotubes into micro-electro-mechanical systems

In this paper we present a holistic wafer-level manufacturing process for nanoscopic sensor devices based on individualized single-wall carbon nanotubes (SWCNTs) integrated in MEMS. The fabrication technology is demonstrated in detail. Moreover, a first application in form of a MEMS test stage for SWCNT strain and reliability experiments is shown.

Deformation measurements of high speed MEMS with sub-picosecond pulses using combined digital holographic two-wavelength contouring and single phase reconstruction

Circular and rectangular MEMS optical scanners operating at a resonance frequencies close to 1 kHz are investigated by single-pulse digital holographic two-wavelength contouring. Coverage of the range interesting for shape measurements of micro mechanical applications like optical scanning mirrors between 10 - 100 μm using only one laser source is a challenging task. For this purpose, a dual-wavelength laser source was developed that generates two 12 nm and 34 nm separated sub-picosecond pulses around 790 nm. A Twyman-Green interferometer was extended by a polarization encoding sequence to separate the interferograms for the recording process. The two holograms were captured simultaneously introducing two CMOS-cameras in the interferometer setup. The phase difference information of the object within the synthetic wavelength of 40 μm was unambiguously generated and the 3D-shape calculated. To reliably measure the surface deformation of the oscillating mirrors the evaluation of the single phase images is sufficient. The resulting deformation of the mirrors based on the reconstructed single phase from the holograms was captured at a wavelength of λ = 783 nm. The deduced rms-values of the surface shape of the oscillating mirrors at maximum load are only ~50 nm, corresponding to a surface flatness of better than λ/10. This is an excellent result, keeping in mind that the mirror plates of the optical scanners are only ~50 μm thick. These detail information from one interferogram are combined with the coarse shape information deduced from the phase difference map of the two interferograms captured at different wavelengths. Using two-wavelength contouring only for extracting the linear slope of the mirror and combining this with the detail information of the single phase images yields a combined reconstruction. This provides a much more realistic picture of the virtually vanishing deformations of the MEMS optical scanners operated at its resonance. We are not aware of any other method that could provide equally detailed information on such a MEMS structure while simultaneously capturing such a large amplitude of the dynamics.