Test Apparatus for Acoustical Transducer
Publication Date: 2004-Oct-06
The IP.com Prior Art Database
Acoustical test apparatus for wafer-level acoustical test of MEMS based transducers
ACOUSTICAL TEST APPARATUS AND METHOD FOR WAFER LEVEL CHARACTERIZATION OF ELECTROACOUSTICAL TRANSDUCERS
FIELD OF THE INVENTION
 The invention relates to an acoustical test apparatus and method for wafer level test of silicone microphones or silicone based loudspeaker devices fabricated by microelectromechanical system (MEMS) techniques. The invention allows characterization of performance of such acoustical transducers on wafer level.
BACKGROUND 011= THE INVENTION
 The ~dvent of silicone transducers such as a MEMS based silicone microphone disclos~d in the present applicant's patent US 6,522,762 that are fabricated by semicpnductor process techniques has led to a need for test apparatuses and m~thodologies that allow rapid, accurate and reliable test and characterization of ~he acoustical devices on wafer level.
SUMMARY OF THE INVENTION
 In a !first aspect, the invention relates to an acoustical test system for silicone wafers acc<l>rding to claim 1. A significant advantage of the invention is the coupling between the loudspeaker means, which generates the acoustical test signal, and the me~surement cavity that allows a well-defined and easily controllable sound pressure to ~e produced inside the measurement cavity and conveyed through the secondlopening to the acoustical component under test. If the acoustical component comprises a silicone microphone, an area of the second opening may advantageously be comparable to a diaphragm area of individual microphones on the wafer. The micrbphone diaphragm area may lie somewhere between 0.25 and 5 mm2 or more prefenably between 0.5 and 2 mm2 which are preferred ranges of diaphragm areas folr silicone microphones suited for application in compact electronics commumication equipment like hearing aids, cellular phones etc.
 The ~butment between the wafer under test and the second opening, or sound outlet, of t'he measurement cavity serves to significantly attenuate external or surrounding acoljJstical noise signals at the acoustical device under test on the wafer, and thus improve a signal to noise ratio of the measurement. This is a significant advanta~e of the acoustic test apparatus according to the invention, since that feature allows reliable and rapid measurements to be made even in noisy environments typic$lly associated with wafer level test equipment. Another
advantage or the clpse spacing between the second sound outlet and microphone under test is that an accurate pressure response, rather than a free-field response, of the microphone itself can be measured.
 The measurement cavity may comprise a calibrated reference microphone, such ~s a % or X or 1/2 inch type pressure microphone, which monitors the sound pressure! level inside the measurement cavity. The sound pressure monitoring operatior of the reference microphone may be utilized to dynamically adjust a test signal applied to th...