MEMS vs. ECM Microphones: A Professional Selection Guide

1.The Evolution of Acoustic Sensors
2.Key Technical Architecture
3.Key Performance Indicators
4.Application Recommendations
5.Bestar: The Full Spectrum Acoustic Relationship
6.Conclusion

The Evolution of Acoustic Sensors
For decades, the Electret Condenser Microphone (ECM) has been the default in applications of consumer and professional audio. Its simplicity in construction, low cost and its reliability in terms of acoustic requirements made it a stalwart in everything from telephone handsets to studio equipment. But over the last decade, MEMS (Micro-Electro-Mechanical Systems) microphones have moved from the fury to folk dominance.
This change can be seen in the way that engineers and product teams now look for solutions. The discussion is no longer about sound capture. Today the requirements are high Signal to Noise Ratio (SNR), uniformity of phase matching across multiple microphone arrays and stable performance in small compact and hot assemblies. Understanding why this shift is taking place requires taking a close look at the fundamental differences between the two technologies.
This blog offers a three-dimensional comparison between MEMS and ECM microphones concerning the core technical architecture, the significant performance features and the applied usage of the microphones.

Key Technical Architecture
ECM: The Traditional Mechanical Strategy
An ECM microphone is composed of 3 primary components: a flexible diaphragm, an electret backplate and a Field-Effect Transistor (FET). When sound pressure waves arrive at the diaphragm it shifts. This mechanical displacement induces a change in the capacitance between the diaphragm and the backplate making an analog electrical signal, which is amplified by the FET.
The architecture is mature and well known. However, it is essentially mechanical in nature. The diaphragm is a physical moving membrane whereas the FET is a discrete component. This translates to ECMs that are larger in size, sensitive to the assembly tolerances, and not necessarily good for automated surface mount soldering processes.
MEMS microphone: The Semiconductor Approach
A MEMS microphone is constructed with the same photolithographic techniques used to manufacture silicon chips. The diaphragm and backplate are etched as topography directly in a silicon wafer. An ASIC (Application-Specific Integrated Circuit) is being integrated with or under the sensing element to perform the signal conditioning functions and in many situations digital output conversion functions.
The result is a small sensor that is consistent and designed from the ground up for modern electronics manufacturing. The silicon structure is not prone to drifting over time as polymer membranes can be until the integration of the ASIC, which means that the output signal is already clean and processed before it leaves the package.

Key Performance Indicators
1. Size and Integration
MEMS microphones are very small in size. Package heights of less than 1mm are the norm. This makes them the sole viable options for True Wireless Stereo (TWS) earbuds, smart glasses and wearables where every millimeter counts. On the contrary, ECMs require a physical larger size. In space constrained designs, they simply are not an option. In devices where size is not an issue, the fact that the ECM is mechanically robust can still be one point in its favor.
2. Acoustic Uniformity and Phase Matching
This is arguably the most important differentiator of modern product design. Multi-microphone arrays for beamforming, Active Noise Cancellation (ANC) and spatial audio processing rely on accurate matching between the microphones. If two microphones in an array contain different sensitivities or phase responses, the algorithm is unable to calculate direction of sound or cancels noise effectively.
MEMS microphones in particular are manufactured with unit to unit sensitivity tolerances of ±1dB, and 1 to 2 degrees are achievable phase matching values. This is a direct result of semiconductor fabrication absorbing precision.
ECMs are constructed from individual mechanical components. Even within the same production batch, there are sometimes 3dB or more of sensitivity variation. For single microphone applications this is accepted. For array designs it poses a selection challenge. Engineers are faced with the choice of either sorting and matching units manually, or degraded array performance. Neither choice is efficient on a large scale.
3. Environmental Stability and Reliability
Temperature is a very important reliability characteristic. Modern PCB assembly relies on reflow soldering where the components go through an oven with temperatures in excess of 260 degrees Celsius. MEMS microphones are constructed out of silicon, so this process is completed natively there. They are perfectly compatible with the standard SMT assembly lines.
Traditional ECMs are polymer based electro-magnetic materials based on polymer electrets materials that exhibit degradation at high temperatures. Most ECMs cannot survive reflow soldering and have to be hand soldered after main PCB assembly. This adds cost, slows production and adds variability.
On electromagnetic interference (EMI), MEMS microphones have an advantage, too. Due to the package-level integration of the ASIC, and the digital output variants which transmit data, not a low-level analog signal, MEMS designs are by nature more resistant to EMI. ECMs generate analog signal with low impedance and this signal may be subject to interference of surrounding circuits, particularly dense layouts of smartphones or IoT board design.
4. Acoustic Performance ( SNR and Acoustic Overload Point)
High-performance ECMs with high diaphragms still maintain a significant advantage in studio and high fidelity recording applications. A large diaphragm is able to gather more acoustic energy, meaning sensitivity as well as a more natural sound character. This is why the best condenser microphones for vocal recording and instrument recording still use ECM-based large capsules.
However, the gap is getting smaller and smaller. High-performance MEMS microphones are now available with SNR values of over 70dB(A), something that was unthinkable 10 years ago. For voice capture, telecommunication and smart device applications, this level of performance is well enough to cover the requirement. The Acoustic Overload Point (AOP) of modern MEMS devices also regularly exceeds 130 dB SPL so they can also be used in challenging loud environments like concert venues and industrial monitoring uses.

Application Recommendations
1. Choose MEMS
You are designing a smartphone, tablet or laptop device where the feature of SMT compatibility and area limitations would be a non-negotiable. Active Noise Canceling is required for you product. ANC is based on the use of accurate multi-microphone arrays, and only MEMS has the consistency needed.
You are developing a voice assistant device, smart speaker or any product that will use far-field voice capture with the use of beamforming.
Your production volume is high and the efficiency of automated assembly impacts directly upon the unit cost.
The product will be utilized in an environment with high EMI such as around motors or wireless charging circuits or RF components
2. Choose ECM
The product is cost sensitive and uses one microphone in a simple analog audio path. such as a children's toy or a simple intercom system.
You are designing recording equipment on a large-format basis where the size of the diaphragm is contributing directly to the quality of the sound, where the physical limitations of ECM are acceptable.

Bestar: The Full Spectrum Acoustic Relationship
Bestar has a very wide range of acoustic component portfolio to cover both high-performance MEMS microphones and high-reliability ECM solutions. Whether your design calls for the ultra-compact profile offered by a MEMS package for a wearable application or the proven stability offered by an ECM for a cost-optimized application, Bestar provides the correct component with full traceability and production consistency.
In addition to hardware supply, Bestar offers engineering support to the entire acoustic design process. This includes acoustic cavity design and optimization, sensitivity matching for multi-microphone arrays and system level simulation to verify performance before physical prototypes are built. 

Conclusion
The choice between MEMS and ECM is not a decision of which technology is better on an absolute basis. It is then about which technology suits the priorities of your product.
If your design requires compact form factor, good multiproject array performance, applications that are compatible with the SMT assembly method and excellent EMI resistance, MEMS is the obvious choice. The following is a guide covering loudspeaker signal phase: If your application is cost driven, you are using a single microphone channel and are not confined by thermal/space requirements, ECM is still the practical and cost-effective solution.
Define what your product means (performance, size, cost and manufacturing process), then match the microphone technology to those requirements.
Bestar's engineering team is available to assist with your selection process with product specification comparisons, application-specific recommendations and samples of the product line for evaluation. To start the conversation, contact Bestar.