Micromachined Liquid Flow Sensor with Hermetic Sealing
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Solution Overview
Problem
Current liquid flow measurement technologies in microfluidic configurations face challenges due to bulkiness, high cost, and inaccuracy, particularly in medical applications where disposable, cost-effective, and accurate flow sensors are needed to prevent cross-contamination and ensure precise medication dosing.
Innovation Solution
A micromachined liquid flow sensor using silicon dioxide/silicon nitride film as a passivation layer and through-substrate conductive vias for electrical connection, with a rectangular enclosure ring pattern for protection, fabricated using thin film micromachining technology on low-cost substrates like Pyrex or Boron Silica, enabling mass production and hermetic bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical or ultrasonic sensors are used to identify air embolism and measure flow rate, then measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex optical or ultrasonic sensing systems with a simple thermal-based flow sensor that measures flow rate through thermal conduction differences in the fluid stream, significantly reducing device complexity while maintaining measurement capability
Solution Approach 2:
The invention employs a disposable micromachined flow sensor that can be discarded after single use, eliminating the need for complex cleaning, calibration, or maintenance procedures associated with reusable optical/ultrasonic sensors, thereby reducing overall system complexity
2Measurement precision
If Coriolis liquid flow meter is used for flow measurement, then measurement accuracy is improved, but device size and manufacturing complexity increase
Solution Approach 1:
The patent divides the flow sensing function into micro-scale segments within a microfluidic channel, using multiple small thermal sensing elements distributed along the channel rather than a single large Coriolis meter, achieving accurate measurement in a compact form factor
Solution Approach 2:
The invention changes the measurement parameter from mechanical vibration (Coriolis effect) to thermal conduction differences, enabling accurate flow measurement in a much smaller device volume suitable for microfluidic applications
3Object-affected harmful factors
If silicon nitride film is used as passivation layer, then protection against liquid penetration is improved, but adhesion reliability deteriorates
Solution Approach 1:
The patent creates a composite passivation structure by depositing silicon dioxide over silicon nitride, combining the liquid barrier properties of silicon nitride with the superior adhesion characteristics of silicon dioxide, thereby achieving both protection and reliability
Solution Approach 2:
The silicon dioxide layer acts as an intermediary between the silicon nitride passivation layer and the underlying device structures, improving interfacial adhesion and stress distribution while maintaining the liquid barrier function of the silicon nitride
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a cost-effective, reliable, and accurate liquid flow measurement in microchannels with high uniformity and reduced production deviations, suitable for hygienic medical applications, while preventing exposure to flow media and ensuring long-term reliability.
Implementation Method 1
One thin layer of silicon dioxide is deposited before the deposition of silicon nitride layer to enhance the adhesion and reliability of the passivation layer
Implementation Method 2
silicon dioxide/silicon nitride film as passivation layer to protect device from penetration of liquid into device and to avoid damages from erosion
Implementation Method 3
The micromachined liquid flow sensor has a number of through-substrate conductive vias which are applied to electrically connect the functional device on top surface of sensor chip to the bonding pads on bottom surface of sensor chip
Implementation Method 4
The bonding pads on the bottom surface of sensor chip will be as well metal bumping bonded to the bonding pads on PCB to complete the electrical connection with an external circuitry
Implementation Method 5
one extra innovative rectangular enclosure ring pattern, which is routing along the four chip edges to form a rectangular enclosure, is applied to provide a protective shield from flow media for all the bonding pads
Data Source
AI summary
The micromachined liquid flow sensor devices are enclosed with silicon nitride film as passivation layer to protect device from penetration of liquid into device and avoid the damages of erosion or short circuit etc. One thin layer of silicon dioxide is deposited underneath the silicon nitride layer to enhance the adhesion and reliability of the passivation layer for various applications. The incorporation of silicon dioxide film had successfully provided reliable passivation protection especially for microfluidic devices application. In order to avoid flow turbulence caused by wire bonding wires, the wire bonding wires are omitted by deploying through-substrate conductive vias whereas connected to the carrier printed circuit board of sensor chip. The present invention disclosed a novel micromachining process and designed structure to form hermit sealing between the sensor chip and the carrier printed circuit board. The hermit sealing underneath the sensor chip can protect the bonding connections from exposing to liquid flow media and avoid short circuitry or induce undesired chemical corrosion. More particularly, the embodiments of the current invention relates to formation steps of a micromachined liquid flow sensor including passivation and protection of bonding connection to its carrier printed circuit board, which is therefore capable to offer superb accuracy and reliability for liquid flow measurement.