Thermal Anemometry Sensor Element with Intermediary Silicon Layer
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Solution Overview
Problem
Existing sensor elements for thermal anemometry face challenges in achieving high precision due to adjustment offsets between lithography and etching process steps, leading to asymmetrical heat dissipation and imprecise transitions between the semiconductor substrate and diaphragm, which can result in inaccurate mass flow measurements.
Innovation Solution
A semiconductor sensor element with a thin-film diaphragm attached to a silicon layer on the semiconductor substrate, where the silicon layer is structured from the side to improve precision, and a recess is formed between the thin-film diaphragm and the substrate, allowing for precise alignment and reducing the cavity size to enhance mechanical stability and prevent asymmetrical heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithography and etching process steps are precisely adjusted to achieve high precision, then manufacturing complexity and cost increase, but adjustment offsets of approximately 5 μm cannot be avoided
Solution Approach 1:
A support structure (erhaltungsstruktur) is introduced as an intermediary element between the semiconductor substrate and the thin-film diaphragm. This support structure serves as a reference framework that defines the lateral boundaries of the cavity and provides precise alignment references for subsequent lithography and etching steps, thereby reducing adjustment offsets without increasing overall process complexity
Solution Approach 2:
The support structure is formed in advance before the thin-film diaphragm is deposited. By pre-establishing the cavity boundaries and alignment references on the semiconductor substrate, the subsequent deposition and processing steps can be performed with higher precision without requiring complex real-time adjustments
2Manufacturing precision
If the thin-film diaphragm is deposited directly onto the semiconductor substrate, then the transition between substrate and diaphragm is less precise, but the manufacturing process is simpler
Solution Approach 1:
The support structure acts as an intermediary layer between the semiconductor substrate and the thin-film diaphragm. It provides a well-defined surface with precise lateral boundaries that facilitates accurate deposition of the diaphragm, improving transition precision while adding only one structural element to the manufacturing process
Solution Approach 2:
The support structure is selectively formed only in the region where the thin-film diaphragm will be deposited, providing localized precision where needed. The structure defines the exact lateral boundaries of the cavity and provides reference surfaces for alignment, improving local manufacturing precision without complicating the entire device structure
3Measurement precision
If adjustment offsets occur between process steps, then asymmetrical heat dissipation occurs and measurement accuracy decreases
Solution Approach 1:
The support structure serves as a stable reference framework that is formed before the heating element and temperature sensor are deposited. It provides fixed lateral boundaries and alignment references that remain consistent throughout subsequent processing steps, ensuring symmetrical positioning of thermal components and preventing asymmetrical heat dissipation
Solution Approach 2:
By pre-forming the support structure with well-defined lateral boundaries before depositing the heating element and temperature sensor, the alignment references are established in advance. This preliminary action ensures that subsequent lithography and etching steps can be performed with consistent alignment, preventing measurement errors caused by asymmetrical positioning
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
This approach ensures high-precision attachment of heating and temperature sensors, reducing manufacturing costs and improving the accuracy of mass flow measurements by maintaining precise alignment and perpendicular boundaries, thereby enhancing the mechanical stability and reducing unforeseen heat dissipation.
Implementation Method 1
A resistive heating element and a temperature-dependent resistor are attached to the front side
Implementation Method 2
A resistive heating element and a temperature-dependent resistor are attached to the front side
Implementation Method 3
the heating of the diaphragm is a function of a heating power and a flow velocity of the passing medium
Data Source
AI summary
A sensor element for thermal anemometry includes a semiconductor substrate and a thin-film diaphragm attached to the semiconductor substrate and having a front side and a rear side. A resistive heating element and a temperature-dependent resistor are attached to the front side of the thin-film diaphragm. In the area of the rear side of the thin-film diaphragm, the semiconductor substrate has a first recess. A silicon layer including a recess which merges with the first recess of the semiconductor substrate is located between the thin-film diaphragm and the semiconductor substrate.