Low-Profile MEMS Printhead with Backside TSV Electrical Connections
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Solution Overview
Problem
Existing MEMS thermal printheads face challenges in delivering electrical energy to the printing surface while maintaining a sufficiently small print gap, which is crucial for achieving high resolution and uniformity in organic LED film deposition.
Innovation Solution
A thermal, non-contact printhead die is fabricated using an SOI structure with a buried oxide layer and ohmic heaters, where through-silicon via plugs electrically couple the heaters to UBM pads, allowing for precise ink delivery and sublimation onto a substrate with a print gap of 10-100 microns, enabling superior film morphology and feature resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If external conductors are used to deliver electrical energy to the printing surface, then electrical connection is achieved, but the print gap cannot be reduced sufficiently
Solution Approach 1:
The patent transitions from planar electrical connections to three-dimensional vertical connections by drilling through-silicon vias (TSVs) from the front surface through the bulk silicon to the backside. This vertical dimensionality allows electrical conductors to be positioned away from the printing surface, enabling reduced print gap while maintaining electrical connectivity.
Solution Approach 2:
The patent extracts external conductors from the printing surface area and relocates them to the backside of the substrate through TSVs. This extraction removes the spatial conflict between conductors and the printing surface, allowing the print gap to be minimized without compromising electrical connection.
2Manufacturing precision
If the print gap is reduced to 10-100 microns for high-resolution printing, then film morphology and resolution improve, but delivering electrical energy becomes difficult
Solution Approach 1:
The patent resolves the energy delivery challenge by utilizing the vertical dimension through TSVs that penetrate the entire silicon bulk. This allows electrical energy to be delivered through the backside of the substrate, completely separating the electrical conduction path from the minimal print gap at the front surface, thus enabling both high resolution and effective heating.
3Reliability
If through-silicon via plugs are used to connect ohmic heaters to UBM pads, then electrical connection through buried oxide layer is achieved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces complex mechanical routing and wiring through the buried oxide layer with a more straightforward approach: drilling TSVs through the front surface, forming simple plug structures, and filling with conductive material. This substitution of mechanical routing with direct vertical penetration simplifies the overall manufacturing process while achieving reliable electrical connection.
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 enables precise deposition of organic LED layers with improved film morphology, uniformity, and feature resolution, addressing the limitations of existing MEMS thermal printheads by eliminating external conductors and achieving a minimal print gap.
Implementation Method 1
The ink is then heated in stages. The first stage evaporates the solvent. During the second stage, the ink is heated rapidly above its sublimation temperature until the organic ink materials evaporate to cause condensation of the organic vapor onto the target substrate.
Implementation Method 2
the organic ink materials evaporate to cause condensation of the organic vapor onto the target substrate
Implementation Method 3
The ohmic heater may be electrically coupled to the UBM pad through the buried oxide layer by means of a through-silicon via ('TSV') plug
Implementation Method 4
An interconnect metal, such as a titanium-tungsten-aluminum layer, may be formed to couple the TSV plug to the UBM pad and to the ohmic heater
Data Source
AI summary
A thermal printhead die is formed from an SOI structure as a MEMS device. The die has a printing surface, a buried oxide layer, and a mounting surface opposite the printing surface. A plurality of ink delivery sites are formed on the printing surface, each site having an ink-receiving and ink-dispensing structure. An ohmic heater is formed adjacent to each structure, and an under-bump metallization (UBM) pad is formed on the mounting surface and is electrically connected to the ohmic heater, so that ink received by the ink-delivery site and electrically heated by the ohmic heater may be delivered to a substrate by sublimation. A through-silicon-via (TSV) plug may be formed through the thickness of the die and electrically coupled through the buried oxide layer from the ohmic heater to the UBM pad. Layers of interconnect metal may connect the ohmic heater to the UBM pad and to the TSV plug.