Marc-Peter Schmidt

Towards a SAW based phononic crystal sensor platform

A Surface Acoustic Wave (SAW) sensor platform based on phononic crystals specifically designed for chemical and biosensing will be introduced. The unique feature of this sensor concept is the possibility to determine volumetric properties of analytes at volume as low as 1 nl. The sensor platform has the capability paving the way to study chemical reactions in microreactors or biomaterials directly in their physiological environment without any label.

A novel injection molded fluidic interposer for microfluidic applications

The implementation of fluidic functions in 3D-MID (three dimensional molded interconnect devices) allows to create a new field of applications and enhanced system solutions. We report about the capabilities of MID for the packaging of chip modules with microfluidic functions. A mechanically stable and leak tight fluidic connection is needed between the microfluidic chip and the environment. For this purpose a fluidic interposer is fabricated by the LDS-process (laser direct structuring) and includes a metallization for electrical signals and channel structures for fluidic features. The presented interposer enables the transformation of fluidic ports from the macro- to the micro scale. To characterize the device, a microfluidic test chip made of silicon and glass (Borofloat®) has been fabricated and mounted on the fluidic interposer by a flip-chip vapor phase process. Finally the potential of the system is shown by testing maximum pressurization and fluidic sealing.

Phononic crystal based liquid sensor governed by localized defect resonances

Phononic crystal sensors are promising for liquid sensor applications. We have already shown that the frequency of narrow transmission bands depends on properties of liquids confined within a 2D phononic crystal. In comparison to almost all liquid sensor platforms where sensors respond to effects close to the sensor surface, e.g. mass load due to absorption of molecules in a recognition layer, the objective of the liquid cavity resonators is the determination of volumetric (bulk) properties of the liquid. The quality factor is the most crucial parameter of sensor performance. Therefore, classical microacoustic resonance sensors must avoid radiation of acoustic energy into the liquid. The phononic crystal sensor concept tailors acoustic wave propagation in a way to excite a specific mode within the band gap of the phononic crystal. We apply surface acoustic wave (SAW) devices as reliable platform for the realization of phononic crystal sensor. It performs both excitation of a selected liquid cavity resonance and its detection. The liquid cavity microchannel is realized within an overlayer of the SAW device. The liquid in the microchannel becomes a part of vibrating overlayer and determines its acoustic properties. The sensor development contains three parts: development of the SAW platform including etching of periodic elements, design of the overlayer containing the microchannels, and optimization of acoustic coupling between the two elements. We present simulation results of the overlayer with the acoustic field penetrating the liquid. We further report on technology to realize phononic crystal structures with well-defined shape and depth of etched structures in SAW substrates which prove the correctness and feasibility of our approach.

SAW-Based Phononic Crystal Microfluidic Sensor—Microscale Realization of Velocimetry Approaches for Integrated Analytical Platform Applications

The current work demonstrates a novel surface acoustic wave (SAW) based phononic crystal sensor approach that allows the integration of a velocimetry-based sensor concept into single chip integrated solutions, such as Lab-on-a-Chip devices. The introduced sensor platform merges advantages of ultrasonic velocimetry analytic systems and a microacoustic sensor approach. It is based on the analysis of structural resonances in a periodic composite arrangement of microfluidic channels confined within a liquid analyte. Completed theoretical and experimental investigations show the ability to utilize periodic structure localized modes for the detection of volumetric properties of liquids and prove the efficacy of the proposed sensor concept.

Test Chip for Characterization of Mechanical Stress Caused by Packaging Processes

This paper reports on a method for estimation and minimization of mechanical stress on MEMS sensor and actuator structures due to packaging processes based on flip chip technology. For studying mechanical stress a test chip with silicon diaphragms was fabricated. A network of piezo-resistive solid state resistors created by diffusion was used to measure the surface tension pattern between adjacent diaphragms. Finite element method simulation was used to calculate the stress profile and to determine the optimum positions for placing the resistive network

SAW based phononic crystal liquid sensor - Periodic microfluidic channels approach

We report on practical realization of novel liquid sensor upon a base of typical SAW device design. The sensor is implemented as a periodic microfluidic structure atop a piezoelectric substrate. Simultaneous employment of phononic crystal phenomenon and structural resonance inside the phononic crystal is the basic idea behind. The phononic crystal band gap prevents propagation of traveling waves through the structure and their conversion and scattering into the substrate. The structural resonance enables acoustic signal amplification at frequencies predetermined by materials composing the structure. The sensor operates at high frequencies and potentially is capable to measure sound velocity and bulk viscosity of liquids with a precision superior to established instruments. The periodic microfluidic structure is made of SU-8 layers atop of lithium niobate based SAW device and acts as a liquid analyte container. It applies MEMS technology with a specific attention to the multilayer fabrication and exceptional parameters control. Experimental results demonstrate the feasibility of this approach providing a distinct and predictable sensor response on speed of sound of analyte.

Technology towards a SAW based phononic crystal sensor

Phononic crystals (PnC) with a specifically designed defect have been recently introduced as novel sensor platform. Those sensors feature a band gap covering the typical input span of the measurand as well as a narrow transmission peak within the band gap where the frequency of maximum transmission is governed by the measurand. This innovative approach has been applied for determination of compounds in liquids [1]. Improvement of sensitivity requires higher probing frequencies around 100 MHz and above. In this range surface acoustic wave devices (SAW) provide a promising basis for PnC based microsensors [2]. The respective feature size of the PnC SAW sensor has dimensions in the range of 100 μm and below. Whereas those dimensions are state of the art for common MEMS materials, etching of holes and cavities in piezoelectric materials having an aspect ratio diameter/depth is challenging. In this contribution we describe an improved technological process to manufacture considerably deep and uniform phononic crystal structures inside of SAW substrates.

A microfluidic interposer based on three dimensional molded substrate technology

Three dimensional molded interconnect devices (MID) with fluidic features offer new possibilities for the packaging of microfluidic components. This paper reports about an MID based fluidic interposer to bridge the micro-macro gap of fluid delivery in microfluidic systems. The interposer is fabricated by standard MID fabrication technology and includes a metallization for electrical signals and channel structures for fluidic functions. A microfluidic test chip is assembled to the interposer by a flip-chip process. The proposed interposer is suitable for pressure and capillary driven flows. Results from pressurization testing with liquids and gases are given.