Avoiding Touch Sensor Patent Traps: OGS Technology with Bridges Outside the Active Area

Introduction: The "Achilles' Heel" of SITO

In the field of touch sensors, SITO (Single-sided ITO) has long been favored for high-end touch panels due to its thinness and high light transmittance. However, this technology has a long-standing "Achilles' heel" – the visibility of the bridge structure.

In a SITO structure, the drive lines (X-axis) and sense lines (Y-axis) are on the same side of the substrate, inevitably requiring a "bridge" structure at electrode intersections, using an insulating layer and conductive bridge to avoid short circuits. The problem is: when light hits the bridge area, due to differences in refractive index and reflectivity between the transparent electrode (ITO) and the insulating layer, the bridge points become clearly visible, affecting display quality.

In a 2015 patent application, Apple attempted to use "Multiple Bridges" to improve optical uniformity, but never fully resolved the optical defects inherent to the bridge structure itself.

So, is there a way to completely "eliminate" bridges inside the active area? The answer is: move the bridges outside the active area.

I. Core Pain Points of Traditional SITO Bridges

In traditional SITO structures, bridges are located inside the Active Area, presenting three major problems:

1. Optical Visibility

OGS (One Glass Solution) touch screens fabricate the touch structure directly on the cover glass. When light hits the bridge structure, due to differences in transmission and reflection of light through the transparent electrode and insulating layer, the bridge points are easily perceived by the human eye. As noted in BOE's patent CN104238818A: "Bridge points are easily seen; the wider the bridge line width and the thicker the insulating layer, the more obvious the visibility."

2. Step Coverage Breakage Risk

The bridge structure requires a "step coverage" path at the edges of the insulating layer. In actual manufacturing, the transparent electrode is prone to breakage and collapse at bridge points due to excessive step angles, leading to electrical connection failure. This problem is particularly acute in narrow-bezel, high-precision devices.

3. Parasitic Capacitance Interference

Parasitic capacitance arises between the metal bridge and surrounding electrodes, affecting touch sensitivity. Research by Korea's Dongwoo Fine Chem shows that reducing the width of the bridge extension can lower parasitic capacitance, but this adjustment increases resistance, requiring a difficult trade-off.

II. A Breakthrough Idea: Bridges Outside the Active Area

To fundamentally solve the above problems, the most direct method is to "exile" bridges from the active area. The logic behind this idea is:

DITO's advantage lies in the natural isolation of its two layers, requiring no bridges inside the active area, but it needs two ITO coatings. SITO's advantage lies in its single ITO layer, lower cost, but it requires bridges inside the active area. So, can we move SITO's bridges outside the active area and get the best of both worlds?

The answer is yes. This design concept has been reflected in recent patents.

III. Technical Solution: DITO Structure with "Bridges Outside the Active Area"

3.1 Basic Architecture: Repurposing DITO

The foundation of this solution is the DITO (Double-sided ITO) structure – where drive lines and sense lines are on opposite sides of the substrate. Since the two layers are naturally isolated by the glass substrate, bridges are originally unnecessary.

However, "bridges" here refer specifically to electrode crossovers inside the active area. In fact, in a DITO structure, there are still scenarios where "bridges" are needed – for example, when routing drive signals from outside the active area into the active area, they may need to cross sense lines.

3.2 Core Innovation: Bridges Relocated Outside

The specific implementation is as follows:

Step 1: Inside the active area of the substrate, use a DITO structure – drive lines (X-axis) on one side, sense lines (Y-axis) on the other, naturally insulated, requiring no bridges.

Step 2: Route the drive lines and sense lines outwards to the left and right sides respectively, outside the active area.

Step 3: Outside the active area (i.e., the bezel region), bridge structures are used to connect portions of the same line that need to cross another line. Since these bridges are located in the bezel area, covered by black matrix (BM), they are completely invisible – therefore there is no optical visibility issue.

3.3 Key Manufacturing Points

· Bridge Location: Bridge structures are placed outside the active area, i.e., in the bezel region of the substrate.

· Bridge Type: Top Bridge structure – an insulating layer is first formed on the electrode layer, then a metal bridge is fabricated on the insulating layer.

· Material Choice: Bridge materials can be low-resistance metals (e.g., Mo/Al/Mo), no longer constrained by transparency requirements.

· Cover Layer: The bridge area is completely covered by BM (Black Matrix), invisible to the user.

IV. Solution Advantages

V. Patent Traps to Beware Of

When implementing this technical solution, special attention must be paid to avoiding the following patent barriers:

5.1 Apple's Basic DITO Patent

Apple's US 7918019 patent systematically protects a method for manufacturing ultra-thin DITO touch sensors. The key to this patent is the "bond-process-separate" process – bonding two thin glass sheets, processing them, then separating to obtain ultra-thin panels. If adopting a DITO structure, caution is needed to determine whether it falls within the scope of this patent.

5.2 BOE / Hefei Xinsheng's Bridge Structure Patent

BOE and Hefei Xinsheng Optoelectronics, in CN104238818A, protect an OGS bridge structure using "one insulating layer + two transparent electrodes." Although this patent targets bridge optimization inside the active area, its core structure – using one insulating layer to isolate two electrode layers – presents overlapping risk with the bridges-outside-active-area solution.

5.3 Apple's Multiple Bridges Patent

Apple, in US 20150077383 A1, proposed a "Multiple Bridges" solution, protecting a design where drive and sense lines are formed on the same layer and connected through multiple bridge points. If the bridges-outside-active-area solution uses multiple bridge points to reduce resistance, it needs evaluation against this patent's scope.

5.4 Dongwoo Fine Chem's Parasitic Capacitance Optimization Patent

Korea's Dongwoo Fine Chem, in US 20200089352 A1, protects a technology for reducing parasitic capacitance by reducing the width of bridge extensions. Although this patent aims to solve a problem, its feature of "the bridge electrode includes an extension with a width smaller than that of the end portion" could become an obstacle to design-around.

Bastron's Path as a Pioneer

According to industry records of technological development:

· Timeline: In 2012, Bastron filed an invention patent application with the China National Intellectual Property Administration (CNIPA) regarding "bridges outside the active area." The core of this patent is precisely the technical solution described herein – moving all bridge structures originally located inside the active area of a SITO structure to the bezel region covered by black matrix (BM), thereby completely solving the optical visibility problem of bridges.

· Product Implementation: At the same time as or shortly after filing the patent application, Bastron had already applied this technical solution to the design and manufacturing of actual products. This means that the technology not only existed on paper but was also publicly sold on the market, constituting "public use" in the legal sense.

· Examination Process: During substantive examination, the examiner cited relevant patents or pre-research results from international giants such as Apple and Samsung as prior art, arguing that the invention lacked novelty or inventive step. Bastron submitted multiple arguments and amended texts, but ultimately the patent was not granted.