Pressure is one of the most widely measured physical parameters in modern electronic systems. From monitoring blood pressure inside medical equipment to measuring air pressure in aerospace systems, engineers increasingly need sensors that combine small dimensions with high sensitivity and repeatable performance.
MEMS pressure sensors provide one solution. Manufactured using semiconductor and microfabrication techniques, these devices use microscopic mechanical structures to convert changes in pressure into measurable electrical signals.
For a broader introduction to Micro-Electro-Mechanical Systems, including accelerometers, gyroscopes and other sensor types, see ICT’s existing guide, What is a MEMS Sensor?. This article focuses specifically on pressure sensors and, in particular, the MEMS manufacturing processes that influence their performance.
The relationship between silicon wafers, diaphragm dimensions, wafer thickness, surface quality, thin-film structures and precision dicing illustrates why manufacturing control is so important when producing these miniature devices.
The Basic Principle Behind a MEMS Pressure Sensor
At the heart of many MEMS pressure sensors is a very thin diaphragm.
This microscopic membrane is designed to deflect when there is a difference in pressure between its two sides. The amount of movement may be extremely small, but the sensor incorporates structures capable of converting that mechanical deformation into an electrical measurement.
Silicon is particularly important in pressure sensor fabrication. Single-crystal silicon has useful mechanical properties and is compatible with established semiconductor processing techniques, allowing diaphragms, cavities, electrical structures and other features to be manufactured at wafer level. (PubMed Central (PMC))
Rather than manufacturing each sensor individually, numerous sensor structures can be fabricated across a silicon wafer before being separated into individual dies.
This wafer-level approach makes processes such as wafer preparation, thinning, deposition and dicing particularly important to the final device.
How the Silicon Diaphragm Measures Pressure
A typical MEMS pressure sensor contains a cavity beneath or adjacent to its flexible diaphragm.
When the pressure on one side of the diaphragm differs from the reference pressure on the other, the diaphragm bends. Its dimensions and mechanical properties determine how it responds.
Depending on the design, MEMS pressure sensors can measure absolute, gauge or differential pressure.
An absolute pressure sensor compares the measured pressure with a sealed reference, typically a vacuum or controlled reference pressure. Gauge sensors measure relative to ambient pressure, while differential sensors compare pressures applied to two separate ports.
However, diaphragm movement alone does not produce a useful electronic output. A transduction method is required to measure the deformation.
Two widely used approaches are piezoresistive and capacitive sensing. (PubMed Central (PMC))
Piezoresistive MEMS Pressure Sensors
In a piezoresistive pressure sensor, resistive elements are positioned in areas of the diaphragm where mechanical stress occurs as the membrane bends.
When pressure deflects the diaphragm, the resulting mechanical stress changes the electrical resistance of the piezoresistors. These resistance changes can then be converted into an electrical signal representing the applied pressure.
The positioning of these elements matters. Research into silicon piezoresistive sensors shows that piezoresistors can be located close to diaphragm edges where significant mechanical stresses develop during deflection. (PubMed Central (PMC))
Multiple piezoresistors are commonly incorporated into a Wheatstone bridge arrangement, enabling relatively small resistance changes to produce a measurable electrical output.
For MEMS manufacturing, this means that diaphragm geometry and the location of the sensing structures must be tightly controlled. Small dimensional variations can influence how mechanical stress is distributed through the device.
Capacitive MEMS Pressure Sensors
Capacitive pressure sensors measure diaphragm movement differently.
Conductive surfaces form electrodes separated by a small gap. One electrode can be incorporated into or associated with the flexible diaphragm, while another remains relatively fixed.
Together they act as a capacitor.
When pressure causes the diaphragm to move, the distance between the electrodes changes. Because capacitance is related to electrode area and the separation between the electrodes, this movement produces a change in capacitance that can be measured electronically. (PubMed Central (PMC))
Some designs incorporate cavities, insulating layers, deposited metal electrodes and wafer bonding. One published capacitive sensor design, for example, used an SOI wafer to create a silicon diaphragm alongside sputtered aluminium electrodes and deposited silicon dioxide insulation. (PubMed Central (PMC))
These structures demonstrate how MEMS performance can depend upon several manufacturing processes working together rather than on a single fabrication stage.
Why Wafer Thickness Matters
One particularly important consideration is thickness.
The dimensions of the pressure-sensitive diaphragm influence its mechanical response to pressure. Diaphragm thickness is therefore a design parameter rather than simply a consequence of how the wafer happens to be processed.
Different MEMS devices can require very different thicknesses depending upon their operating pressure range, diaphragm dimensions, required sensitivity and overall architecture. Published MEMS pressure sensor designs range from very thin micrometre-scale diaphragms to substantially thicker structures for different applications. (PubMed Central (PMC))
Thickness control can also become important at wafer level.
Processes including back grinding, lapping, polishing and controlled etching may be used at different stages of MEMS fabrication to create the required dimensions and surface condition.
ICT’s wafer processing capabilities include precision back grinding to reduce wafer thickness down to 100 µm, supporting applications including MEMS sensors where compact dimensions and controlled wafer geometry are required. (ict-ltd.co.uk)
Surface Quality and MEMS Manufacturing
Thickness is only part of wafer preparation. Surface quality, flatness and thickness uniformity can also affect downstream manufacturing.
Processes such as precision lapping remove controlled amounts of material while improving dimensional consistency. Surface preparation can also remove damage associated with earlier processing and provide an appropriate foundation for subsequent fabrication stages.
ICT uses controlled lapping and polishing processes for semiconductor and MEMS applications, supported by metrology for verifying dimensions, flatness and surface condition. (ict-ltd.co.uk)
This becomes increasingly important when structures are small and tolerances are tight. Variations that appear insignificant at a conventional engineering scale can become much more significant when working with micro-scale mechanical devices.
The Role of Thin Films
MEMS pressure sensors are rarely composed solely of a shaped piece of silicon.
Depending on their design, they can contain multiple functional thin films used for electrodes, interconnections, insulation, passivation or sensing structures.
Materials including aluminium, gold and other metals may be deposited onto precisely defined areas of the wafer. Dielectric materials such as silicon dioxide can provide electrical insulation or form part of the device structure.
Research examples demonstrate how sputtered aluminium layers can be incorporated into both piezoresistive and capacitive MEMS pressure sensor fabrication. (PubMed Central (PMC))
Thin-film uniformity, adhesion, thickness and surface condition can consequently become important considerations during MEMS manufacturing.
ICT provides in-house thin-film deposition alongside wafer processing, dicing and other micro-manufacturing capabilities, enabling multiple stages of specialist component manufacture to be coordinated within the same facility. (ict-ltd.co.uk)
Precision Dicing: From Wafer to Individual Pressure Sensor
After wafer-level fabrication has been completed, the individual MEMS devices normally need to be separated.
This is the role of precision wafer dicing.
A processed wafer may contain numerous sensor dies positioned closely together. Cuts must follow defined streets between devices without damaging sensitive structures.
For MEMS pressure sensors, this can be particularly challenging because the wafer may contain delicate diaphragms, cavities, thin films, bonding interfaces or other microstructures.
Poorly controlled dicing can introduce edge chipping, cracking, contamination or mechanical stress. Careful selection of the blade and parameters including spindle speed, feed rate and coolant flow helps minimise these risks.
Published MEMS pressure-sensor fabrication processes commonly include wafer dicing as the final step before individual dies are packaged or assembled. (PubMed Central (PMC))
ICT provides precision dicing of silicon and other specialist substrates up to 200 mm diameter, with processes tailored to customer materials and dimensional requirements. (ict-ltd.co.uk)
Where Are MEMS Pressure Sensors Used?
The small dimensions and electronic integration possible with MEMS technology allow pressure sensors to be incorporated into applications where conventional mechanical pressure sensors may be too large or unsuitable.
Medical and healthcare devices are an important example. Miniaturised pressure sensing can support applications including catheter-based measurements, respiratory equipment, infusion systems and other diagnostic or monitoring technologies.
Aerospace and defence systems can use MEMS pressure sensors for environmental monitoring, altitude-related measurements, airflow measurement and other sensing functions where low mass and compact dimensions are valuable.
Industrial systems use pressure sensing for process monitoring, pneumatic equipment, pumps, filters and fluid-control applications. Capacitive MEMS pressure sensors, for example, have been commercialised for monitoring filter clogging in air-conditioning equipment. (PubMed Central (PMC))
MEMS pressure sensing is also relevant to automotive electronics, environmental monitoring, wearable technology and research instrumentation.
Universities, research organisations and technology start-ups are additionally developing specialised MEMS sensors for emerging applications where conventional off-the-shelf components cannot provide the required dimensions, materials, pressure range or packaging arrangement.
Supporting MEMS Pressure Sensor Development
The operating principle of a MEMS pressure sensor can appear relatively straightforward: pressure bends a microscopic diaphragm and that deformation is converted into an electrical signal.
Manufacturing the structure reliably is considerably more demanding.
Wafer thickness can influence device geometry. Surface condition can affect subsequent fabrication. Thin films must perform their intended electrical or structural function, while precision dicing must separate finished dies without compromising delicate microstructures.
This is why MEMS manufacturing often requires several closely controlled processes rather than one isolated machining operation.
ICT has over 30 years’ experience in precision engineering and provides in-house capabilities including wafer processing, wafer dicing, precision lapping, thin-film deposition, wire bonding and micro assembly. The combination is particularly suited to R&D, prototype and low-to-medium-volume projects where customers require flexibility alongside tight process control. (ict-ltd.co.uk)
For universities, research organisations, medical technology developers, aerospace and defence companies, bioelectronics specialists and start-ups developing new MEMS devices, access to these complementary processes can help bridge the gap between an experimental sensor design and a repeatable manufactured component.
