Technologies

During the early nineties, Sensonor developed its triple stack hermetic wafer bonding technology that has shown extremely good long term properties. In short, the technology is based on a combination of micro machined single crystalline silicon and micro machined borosilicate glass wafers. These wafers are then bonded together using anodic bonding in combination with creating electrical connections into the bonded cavity using semiconductor diffusions buried under a layer of epitaxial silicon. In combination with buried piezo resistors and reactive ion etching, this technology combination is named TP4 and the key features are characterized by:

• Precise control of membrane and or mass thickness by use of electrochemical etch-stop
• Epitaxial layer for mono crystalline thin membranes and beams
• Release etching of masses and moving structures by reactive ion etching (RIE)
• Patented sealed and vented cavities by means of
  - Glass micromachining
  - Triple-stack glass-silicon-glass wafer bonding
• Patented buried conductor crossings of bonded areas
• Piezo resistive detection by means of
  - Long-term stable buried (under epitaxial layer) piezo resistors
  - Sensitive surface piezo resistors
• Thermal excitation and thermo-pneumatic actuation

In one single device, it is possible to realize membranes with two different thickness values. The thinner membranes can be perforated by a dry etching step, thus enabling the production of beams, cantilevers, flexures or other moving structures, possibly in combination with mass elements or other rigid parts.

For our gyro products additional features like capacitive sensing and electrostatic actuation is used using metal electrodes on glass and vertical glass to silicon contact solutions. This technology generation is named TP5.

The importance of utilizing mono crystalline materials like single crystalline silicon cannot be underestimated. Such ideal materials are stronger than steel and almost ideal elastic and perform extremely well electrically compared to poly and amorphous materials.

For the next generation products Sensonor develops new technology modules built on the TP4 and TP5 platforms. These new solutions add features, but at the same time secure the same unique capabilities and reliability as proven by the established platforms.

Part of the new technologies have been developed in collaboration with partners within the EU 6th FP, 2006 - 2009, program e-CUBES (ecubes.epfl.ch) focusing on the development of key micro-system technologies for 3D integration of various heterogeneous integrated process layers and the national RCN (Research Council of Norway) funded program "3D Heterogeneous Micro-Nano Systems".

Of particular interest for our new product development is plasma etching or Reactive Ion Etching (RIE) of dielectric films and Deep RIE (DRIE) of silicon. Compared to wet etching RIE enables new possibilities such as etching of vertical structures independent of the crystal structure in the material and to etch delicate structures without exposing them to liquids that might ruin the structures by breakage or sticking particles.

Also of most importance are additional modules to our wafer bonding technology to enable building complex structures consisting of several wafers and for chip-to-wafer bonding. Among new technologies explored are thermo compression wafer scale bonding of gold-to-gold, adhesive wafer bonding using BCB, eutectic wafer scale bonding of AuSn and AuSi and Solid-Liquid Inter Diffusion technology using SnCu-Sn.

In general Sensonor's products are micro systems built by the combination of a heterogeneous MEMS sensing-actuating die and a mixed-mode (both analogue and digital) ASIC (application specific integrated circuit)assembled and connected into the same sensor housing. The design of the ASIC function is an integrated part of the product development task and the final manufacturing of the actual ASIC die is conducted by world recognized foundries. The heterogeneous MEMS die is manufactured in-house at Sensonor.

All Sensonor development programs rely heavily on an extensive concept and feasibility phase using model and simulation tools to fully understand the complete system including the heterogeneous MEMS structure and the integrated CMOS circuitry (ASIC). Such simulations typically include mechanical, thermal, optical, electrostatic and other properties to ensure that the component is optimized with respect to its application.

Sensonor controls a number of patents for key technologies and solutions and pursues an active IPR strategy.