Thomas Bever

Silicon microphone based on surface and bulk micromachining

In this paper a silicon microphone which can be fabricated using standard semiconductor processes is presented. The acoustic-electrical transducer is based on the capacitance change of a movable 400 nm thin poly-silicon membrane with different diameters (800-1200 µm). A source follower was integrated to transform the impedance. The complete chip is 2×2×0.5 mm3 in size. The sensitivity achieved is in the range of 0.4 to 3.2 mV Pa-1.

Silicon micromachined microphone chip at Siemens

Applications ranging from hearing aids over communication to noise cancellation open up a high volume market for low‐cost, batch producible and reliable microphones. To obey these conditions, a single‐chip capacitive microphone has been developed at Siemens, utilizing a modified standard CMOS process with adjacent bulk micromachining. In a first step, the microphone is integrated with a source follower, enabling low output impedance of the signal. The technology allows for the future integration of advanced circuitry. The microphone consists of an acoustically sensitive polycrystalline silicon membrane and a highly perforated back‐plate as the counter electrode. To achieve highly sensitive devices, special emphasis was given to the stress of the polycrystalline silicon membrane, which should be slightly tensile. Another key issue during the fabrication and in operation is to prevent stiction of the sensitive membrane. Since the overall chip size is below 3‐mm side length, surface mounting in low‐cost SMD packages is possible.

Integrated Giant Magneto Resistors — a new Sensor Technology for Automotive Applications

The paper will give an introduction to the principle of the giant magneto resistive — GMR — effect and the silicon system integration of GMR sensors. The two main applications of a GMR are as a magnetic field strength sensor and as an angular field direction sensor. They will be discussed under consideration of automotive requirements.

Solutions for Tire Pressure Monitoring Systems

The demand for tire pressure monitoring systems is driven by increasing comfort and safety requirements. In order to make such systems available to a wide market, cost optimized solutions are necessary. Costs can be reduced by high integration, low power consumption, small size of the module and the reduction of components by monolithically integrated and intelligent on-chip algorithms.

Diffusion based degradation mechanisms in giant magnetoresistive spin valves

Spin valve systems based on the giant magnetoresistive effect as used, for example, in hard disks and automotive applications consist of several functional metallic thin film layers. We have identified by secondary ion mass spectrometry two main degradation mechanisms: one is related to oxygen diffusion through a protective cap layer and the other one is interdiffusion directly at the functional layers of the giant magnetoresistive stack. By choosing a suitable material as cap layer (TaN), the oxidation effect can be suppressed.