June 28, 2021by Jacob Doughty

Ex parte Hwang, is a recent decision of the Patent Trial and Appeal Board (PTAB) addressing whether a claimed sequence of layers was rendered obvious by a similar sequence of layers in the prior art.

In Ex parte Hwang, the claim at issue was directed to a barrier film used to protect a display device, such as a liquid crystal, electronic ink, or organic light emitting diode (OLED) type device. The relevant claim recited, in part:

A barrier film comprising:

a stacked sheet having a top surface and a bottom surface and comprising:

at least two first layers formed of a semicovalent inorganic material; and

at least one second layer formed of an ionic inorganic material,


each second layer is disposed between two first layers with one first layer in contact with a first surface of the second layer and the other first layer in contact with an opposite second surface of the second layer,

each first layer and second layer are alternately disposed, the first layers are disposed to form both the top and bottom surfaces of the stacked sheet…

the difference in binding energy between the semicovalent inorganic material and the ionic inorganic material is in the range of 0.1 eV to 3.9 eV…

Thus, the claim was directed to a film including a stack of alternating layers of a first material and second material, with a layer of the first material at the top of the stack and the bottom of the stack:

1—2—1; or


In rejecting the claim, the examiner relied on a prior art reference disclosing a similar sequence of layers in a barrier film. However, in the prior art reference, the alternating layers were joined by “anchor coat” layers for “improving interlayer adhesiveness between two layers.” The prior art reference disclosed, for example:


Applicant argued the first layers could not be “in contact” with the second layers because of the presence of the anchor coat layers.

The PTAB noted that the examiner must give broadest reasonable meaning to “contact” and that such term was not defined in the specification. Interestingly, the PTAB noted that applicant added the requirement of contact to the claim during prosecution, relying for support on the description of sequential deposition of first and second layers in an actual example. Ultimately, the PTAB relied on a dictionary definition as providing the conventional meaning of “contact” as requiring a “union or junction of surfaces.”

The PTAB concluded that the examiner had impermissibly read the requirement of contact out of the claim and relied on impermissible hindsight in making the rejection over the prior art reference.

Takeaway: The number of patents that are directed to new sequences of layers of known materials would probably surprise a non-practitioner. There is always a tension between defining sequences of layers concretely to distinguish over prior art and being permissive of additional, intervening layers to avoid a design-around. Terms that are seemingly clear – “on,” “over,” “in sequence,” “in contact” – can be the source of disputes during examination and thereafter (“indirect contact”? “contact via”?). To avoid uncertainty (if this is desired), terms defining relative location should be defined explicitly in the specification and used consistently in the claims.

Judges: Colaianni, Dennett, McGee

by Jacob Doughty

Jacob A. Doughty is a patent attorney and founding partner of Element IP. Jacob’s practice includes all areas of US patent law with an emphasis on patent prosecution and management, client counseling, opinion work, and due diligence in the chemical, pharmaceutical, and biotechnology sectors.