In this study we successfully bonded silicon wafer substrates with metal based thermocompression technology. This technology has the advantage of inherent possibility of hermetic sealing and electrical contact. We used three different kinds of metals: gold, copper and aluminum. We will show the hermeticity, bonding strength and reliability of the different processes and compare the results
To increase the yield of the wafer-level Cu-Cu thermo-compression bonding method, certain surface pre-treatment methods for Cu are studied which can be exposed to the atmosphere before bonding. To inhibit re-oxidation under atmospheric conditions, the reduced pure Cu surface is treated by H2/Ar plasma, NH3 plasma and thiol solution, respectively, and is covered by Cu hydride, Cu nitride and a self-assembled monolayer (SAM) accordingly. A pair of the treated wafers is then bonded by the thermo-compression bonding method, and evaluated by the tensile test. Results show that the bond strengths of the wafers treated by NH3 plasma and SAM are not sufficient due to the remaining surface protection layers such as Cu nitride and SAMs resulting from the pre-treatment. In contrast, the H2/Ar plasma–treated wafer showed the same strength as the one with formic acid vapor treatment, even when exposed to the atmosphere for 30 min. In the thermal desorption spectroscopy (TDS) measurement of the H2/Ar plasma–treated Cu sample, the total number of the detected H2 was 3.1 times more than the citric acid–treated one. Results of the TDS measurement indicate that the modified Cu surface is terminated by chemisorbed hydrogen atoms, which leads to high bonding strength.
OCT instruments permit fast and non-invasive 3D optical biopsies of biological tissues. However, they are bulky and expensive, making them only affordable at the hospital and thus, not sufficiently used as an early diagnostic tool. Significant reduction of system cost and size is achieved by implementation of MOEMS technologies. We propose an active array of 4x4 Mirau microinterferometers where the reference micro-mirrors are carried by a vertical comb-drive microactuator, enabling the implementation of the phase-shifting technique that improves the sensitivity and eliminates unwanted interferometric terms. We focus on the design of the imaging system, the microfabrication and the assembly of the Mirau microinterferometer, and the swept-source OCT imaging.
For biomedical applications, smart materials that are used as sensors or actuators have to match some criteria, especially bio-compatibility and softness. Smart polymers are candidates that fulfill these two criteria. A sensitivity to compression is created by adding magnetic particles to a compressible foam polymer. A foam-based composite is fabricated for its small Poisson’s ratio, which enables significant compression, up to 50%. This large compression induces a change in its magnetic properties, which can be detected using coils. By setting the sensing coils as a compact array of 3 × 3, the sensor successfully detected and localized an applied deformation.
The paper presents the multi-wafer bonding technology as well as the integration of electrical connection to the z-scanner wafer of the micromachined array-type Mirau interferometer. A Mirau interferometer, which is a key-component of optical coherence tomography (OCT) microsystem, consists of a microlens doublet, a MOEMS Z-scanner, a focus-adjustment spacer and a beam splitter plate. For the integration of this MOEMS device heterogeneous bonding of Si, glass and SOI wafers is necessary. Previously, most of the existing methods for multilayer wafer bonding require annealing at high temperature, i.e., 1100 degrees C. To be compatible with MEMS devices, bonding of different material stacks at temperatures lower than 400 degrees C has also been investigated. However, if more components are involved, it becomes less effective due to the alignment accuracy or degradation of surface quality of the not-bonded side after each bonding operation. The proposed technology focuses on 3D integration of heterogeneous building blocks, where the assembly process is compatible with the materials of each wafer stack and with position accuracy which fits optical requirement. A demonstrator with up to 5 wafers bonded lower than 400 degrees C is presented and bond interfaces are evaluated. To avoid the complexity of through wafer vias, a design which creates electrical connections along vertical direction by mounting a wafer stack on a flip chip PCB is proposed. The approach, which adopts vertically-stacked wafers along with electrical connection functionality, provides not only a space-effective integration of MOEMS device but also a design where the Mirau stack can be further integrated with other components of the OCT microsystem easily
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.