Silicon microphones, also known as MEMS (Micro-Electro-Mechanical Systems) microphones, have gained significant traction in consumer electronics due to their small size, durability, and ease of integration into digital systems. There are two main classifications of silicon microphones:
1. MEMS IC with ASIC Amplifier
The first classification involves the manufacturing of MEMS ICs by specialized MEMS foundries, combined with an ASIC (Application-Specific Integrated Circuit) amplifier. These MEMS ICs and ASICs are packaged into a silicon microphone chip using a SIP (System in Package) method. In this process, it is critical to protect the diaphragm from damage during packaging, which increases the cost.
2. CMOS-based MEMS Structure
The second classification uses CMOS (Complementary Metal-Oxide-Semiconductor) wafer fabrication to produce the ASIC component first. Then, a MEMS structure is formed using a post-process that creates the diaphragm and cavity. Currently, the MEMS process cannot be fully integrated into standard CMOS wafer facilities due to the need for polymer deposition on the diaphragm, which is not yet standard in semiconductor IC processes.
Once the CMOS process is completed, the diaphragm is etched on the front of the chip, and the cavity and acoustic holes are etched on the back. This process is achieved with the use of a carrier wafer. However, standard CMOS facilities currently cannot create this environment, making the process more complex.
Challenges in Packaging
The major challenge for both MEMS classifications lies in the packaging technology. The patents for MEMS microphone packaging are controlled by a few companies, particularly in the US, leading to a concentration of market share among a few manufacturers.
Marquess Electronics' Approach
Marquess Electronics uses an innovative method where, after the CMOS process, the cavity and acoustic holes are formed from the back of the chip, releasing the MEMS structure. This process doesn't require special equipment or materials, making it feasible within existing CMOS wafer facilities, which helps to lower development costs.
Additionally, Marquess Electronics integrates the CMOS circuitry and MEMS microphone directly onto a single chip using wafer-level packaging technology. This method also avoids damaging the diaphragm during packaging, which can be a common issue with traditional methods.
Advantages of Silicon Microphones
Silicon microphones have largely replaced ECM (Electret Condenser Microphones) in mobile phones, especially smartphones, due to their weather resistance, small size, and ease of digitalization. They are made of semiconductor materials, which are stable and unaffected by environmental changes like temperature and humidity, ensuring consistent sound quality. This durability makes silicon microphones suitable for SMT (Surface Mount Technology) automated assembly, where temperatures can reach up to 260°C, which would otherwise damage ECM diaphragms.
Applications of Silicon Microphones
In addition to smartphones, silicon microphones are also increasingly used in laptops and are being tested in the development of voice-controlled set-top boxes. The digitalized signals from silicon microphones allow for noise reduction, voice beamforming, and echo cancellation, resulting in superior call quality.
