Danny Reuter

Thin Filmencapsulation of microstructures using Sacrificial CF-Polymer

This paper reports on a new method for thin film encapsulation of microelectromechanical systems (MEMS) using plasma enhanced chemical vapor deposited (PECVD) fluorocarbon polymer as sacrificial material and a stress optimized SiO/SiN capping layer. This technique is applicable for a wide range of MEMS technologies - high aspect ratio as well as surface microstructures - it saves die area and enables standard packaging processes such as dicing and pick and place. Beside of the fabrication technology, this paper presents results of a finite element analysis (FEA) regarding the deflection and mechanical stress due to a pressure difference between the cavity and the ambient. The results of the FEA were verified by interferometric measurements on fabricated test structures.

In-process gap reduction of capacitive transducers

This paper presents a MEMS fabrication technique for reducing the trench width of microstructures below the technological limitations of the deep reactive ion etching (DRIE) process, in order to increase the aspect ratio of the sensing electrode gap of capacitive transducers. The in-process trench width reduction is based on the displacement of a substructure actuated by a buckling beam mechanism. Compressive stress causes a longitudinal force in the acting beams which results in the buckling to a predefined direction. This way, the capacitive sensitivity and hence the signal to area ratio of a transverse comb structure could be increased by a factor of 5.

Post-processing gap reduction in a micromachined resonator for vacuum pressure measurement

This paper describes the application of a micromachined resonator to verify the vacuum pressure and sealing of cavities in micromechanical components. We use an electrostatic driven and capacitively sensed bulk silicon resonator fabricated by Bonding and Deep Reactive Ion Etching (BDRIE) technology. The resonator operates at the first fundamental frequency. The damping is used as a degree of the pressure. Transversal comb structures act as squeeze film damping sources. Post-processing gap reduction substructures are used to increase the damping in the vacuum pressure range. This method makes it possible to observe the pressure over the time of smallest gas volumes by monitoring the damping of integrated micro mechanical resonant structures. Therewith it is possible to estimate the hermetic sealing quality of the closed sensor package. A transfer curve with a logarithmic characteristic is measured.

FEM simulation and its application in MEMS design

This paper presents the simulated static and dynamic properties of a micro capacitive transducer by using commercial FEM software - ANSYS. Evaluation of the stress distribution in the stretched membrane of the transducer indicates that the location of the access holes plays an important role for reliable device fabrication and operation. Acoustic simulation shows that the pressure variation in the radiation field of a piston source can be explicitly demonstrated. Experiment results validate the effectiveness of FEM simulation as a useful tool for the design of MEMS devices and rough estimation of their properties.

Hermetic thin film encapsulation of mechanical transducers for smart label applications

For realizing an active smart RFID label monitoring mechanical shock and inclination during transport processes, a capacitive inertial sensor has been developed. Hermetic sealing of the microstructures has been done by a wafer level thin film encapsulation technology based on CF-polymer as sacrificial layer material and a stress-optimized dielectric layer stack as capping material. Long term stability of the thin film encapsulation hermeticity in dependence of the material stack was tested by measuring the pressure inside the package using the pressure dependency of viscous damping between the electrode plates. For the used material stacks containing SiOx(Hy) or SiOx(Hy)/SiNx(Hy) and sputtered aluminum a sufficient hermeticity with leak rates of 2E-10 Pa·l/s and 6E-12 Pa·l/s, respectively, could be achieved.

Tunable resonators with electrostatic self test functionality for frequency selective vibration measurements

In this paper we present an array of tunable resonators for frequency selective vibration measurements. The resonance frequency tuning is carried out by electrostatic forces directly applied to the seismic mass affecting the total stiffness. Frequency selective sensor systems require the exact knowledge of the resonance frequency. Therefore a method of in-system calibration using electrostatic excitation and capacitive vibration detection was investigated. Coupling problems of the excitation signal into the detection path were solved by using two excitation signals 180/spl deg/ out-of-phase and by contacting the substrate with a backside metallization.

Plasmonic dipole nanoantennas on a SiO2/Si substrate and their characterization

In this paper, the results of the successful fabrication as well as the optical backscattering characterization of single plasmonic gold dipole nanoantennas on a SiO2/Si layered substrate are shown. The nanoantennas were designed for a scattering resonance in the NIR range. In contrast to usually used glass substrates, a six inch Siwafer with a thermally oxidized SiO2 layer in combination with an electron beam lithography lift-off fabrication process has been used for the sake of compatibility with microelectronics fabrication processes. In order to achieve high structural resolutions, a bilayer resist system with different exposure sensitivities was realized. In a second step, the entire resist thickness of 540 nm was reduced to 150 nm in a single layer. The SiO2 thickness was chosen in a way that the optical near-field interactions of the nanoantennas with the silicon substrate are decoupled. The SEM characterization of the fabricated structures shows precise nanoantenna geometries with low edge roughness in the case of the bilayer resist system. The aspect ratio of the fabricated nanoantenna structures is slightly decreased compared to the desired value of five. Depending on the applied e-beam exposure dose, an increase of the structural cross-section, i.e. critical dimension of the dipole width, was observed. Furthermore, the single resist layer introduces some structuring issues. The spectral behavior of the nanoantenna structures was investigated with an optical confocal broadband backscattering measurement setup allowing the spectral characterization of single nanoantenna structures. The developed numerical models helped to understand the impact of the manufacturing imperfections providing improved designs.

Approach to combine electron-beam lithography and two-photon polymerization for enhanced nano-channels in network-based biocomputation devices

Although conventional computer technology made a huge leap forward in the past decade, a vast number of computational problems remain inaccessible due to their inherently complex nature. One solution to deal with this computational complexity is to highly parallelize computations and to explore new technologies beyond semiconductor computers. Here, we report on initial results leading to a device employing a biological computation approach called network-based biocomputation (NBC). So far, the manufacturing process relies on conventional Electron Beam Lithography (EBL). However we show first promising results expanding EBL patterning to the third dimension by employing Two-Photon Polymerization (2PP). The nanofabricated structures rely on a combination of physical and chemical guiding of the microtubules through channels. Microtubules travelling through the network make their way through a number of different junctions. Here it is imperative that they do not take wrong turns. In order to decrease the usage of erroneous paths in the network a transition from planar 2-dimensional (mesh structure) networks to a design in which the crossing points of the mesh extend into the 3rd dimension is made. EBL is used to fabricate the 2D network structure whereas for the 3D-junctions 2PP is used. The good adaptation of the individual technologies allows for the possibility of a future combination of the two complementary approaches.

HED-TIE: A wafer-scale approach for fabricating hybrid electronic devices with trench isolated electrodes

Organic-inorganic hybrid electronic devices (HEDs) offer opportunities for functionalities that are not easily obtainable with either organic or inorganic materials individually. In the strive for down-scaling the channel length in planar geometry HEDs, the best results were achieved with electron beam lithography or nanoimprint lithography. Their application on the wafer level is, however, cost intensive and time consuming. Here, we propose trench isolated electrode (TIE) technology as a fast, cost effective, wafer-level approach for the fabrication of planar HEDs with electrode gaps in the range of 100 nm. We demonstrate that the formation of the organic channel can be realized by deposition from solution as well as by the thermal evaporation of organic molecules. To underline one key feature of planar HED-TIEs, namely full accessibility of the active area of the devices by external stimuli such as light, 6,13-bis (triisopropylsilylethynyl) (TIPS)-pentacene/Au HED-TIEs are successfully tested for possible application as hybrid photodetectors in the visible spectral range.

Light-induced magnetoresistance in solution-processed planar hybrid devices measured under ambient conditions

We report light-induced negative organic magnetoresistance (OMAR) measured in ambient atmosphere in solution-processed 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) planar hybrid devices with two different device architectures. Hybrid electronic devices with trench-isolated electrodes (HED-TIE) having a channel length of ca. 100 nm fabricated in this work and, for comparison, commercially available pre-structured organic field-effect transistor (OFET) substrates with a channel length of 20 µm were used. The magnitude of the photocurrent as well as the magnetoresistance was found to be higher for the HED-TIE devices because of the much smaller channel length of these devices compared to the OFETs. We attribute the observed light-induced negative magnetoresistance in TIPS-pentacene to the presence of electron–hole pairs under illumination as the magnetoresistive effect scales with the photocurrent. The magnetoresistance effect was found to diminish over time under ambient conditions compared to a freshly prepared sample. We propose that the much faster degradation of the magnetoresistance effect as compared to the photocurrent was due to the incorporation of water molecules in the TIPS-pentacene film.