Capacitive microphone with a surface micromachined backplate using electroplating technology

Abstract

A technology for surface micromachining of freestanding metal microstructures using metd ekCtrodepOSitiOn On microphone. Electroplating technology has been used to implein copper, which serves as backplate electrode in the condenser microphone. The 1.8 x 1.8"' large microphone diaphragm etching of the substrate wafer. The realized prototypes have a measured sensitivity of 1.4 mV/Pa using a bias voltage of 28 V. The bandwidth is limited by an anti-resonance at 14 kHz which is due to the semi-rigid backplate. The resonance behavior of the backplate structure has been analyzed with finite element modeling with results in good agreement with measured data. 1911[7]. They always involve more or less laborious alignment procedures with an associated reduction in yield. The first surface a sacrificial photoresist layer has been applied to a Condenser ment a suspended and perforated 15-pm-thick microstructure micromachined structures intended for condenser microphone [ l l1-Their were presented by Hijab and diaphragm layer was in PolYsilicon With a CVD oxide as h e sacrificial layer between the diaphragm and the rigid backplate strict of the word, i.e., only one side of the wafer was processed. However, no measured results were ever reported. Lately, results On a new SiliCOn condenser microphone With a major surface micromachining step has been reported by Scheeper et al. [12]. It employs PECVD nitride for both backplate and diaphragm electrodes and a sputtered aluminium layer as a sacrificial air gap spacer. Sensitivities of 1 to 2 mVPa have been obtained at bias voltages up to 16 V. N important number of reports have been published A new interesting tool for the fabrication of surface mion capacitive sensors, such as pressure [I], ac-crostructures on silicon is metal electrodeposition combined celerometers [21 and microphones [31. some of the advantages with resist micropatterning techniques. It has been successfully of capacitive compared to, e.g., the piezoresistive applied to numerous microelectro-mechanical sensors and acsensors, are high sensitivity, low temperature coefficients, tuators [14I-[ 161. Compared to h e polysilicon technologies, and good long-temThis has been demonstrated microstructuring by electrodeposition allows for thicker layers in several of which are now corn-and features with high aspect ratios. The electrodeposition mercially available. The majority of these examples use the technology also offers a greater choice of materials, e.g., well-established technology of bulk silicon micromachining copper, nickel, gold, etc. A p~c u l a r l y useful combination in for he fabrication of the chip. However, progress has capacitive sensor design is electroplating on a sacrificial layer recently been made in surface micromachining of capacitive as Proposed by Mohr et al. [171. Underetching of the sacrificial sensors [4], [5]. The motivation for the research on surface layer leaves a free-standing electroplated structure that may micromachined is the possibility to reduce the size serve as one of the elec...

A 1.8 V 828 μW 80 dB digital MEMS microphone

“…Several MCM readout interfaces have been proposed in the literature [7][8][9][10]; however, the measurement results of a complete digital MCM system integrated in a singlepackage, along with a modeling framework, have not been presented so far according to authors' knowledge. This paper presents the design details and measurement results of a single-package digital MEMS microphone, organized in six main sections.…”

Slotted capacitive microphone with sputtered aluminum diaphragm and photoresist sacrificial layer

“…Typically, a cavity is etched into a silicon substrate by slope (54.74 deg) etching profiles using KOH etching to form a thin diaphragm or perforated back plate (Kronast et al 2001;Pedersen et al 1997;Bergqvist and Gobet 1994;Torkkeli et al 2000;Kabir et al 1999). The forming of a cavity or back chamber from the backside of a wafer by KOH etching is slow and boring in that several hundred micrometers of substrate must be etched to make the chamber.…”

High sensitivity and small size MEMS capacitive microphone using a novel slotted diaphragm

“…Typically, a cavity is etched into a silicon substrate by slope (54.74°) etching profiles using KOH etching to form a thin diaphragm or perforated back plate (Kronast et al 2001;Pedersen et al 1997;Bergqvist and Gobet 1994;Torkkeli et al 2000;Kabir et al 1999). The forming of a cavity or back chamber from the backside of a wafer by KOH etching is slow and boring in that several hundred micrometers of substrate must be etched to make the chamber.…”