Fumitomo Hide, Ph.D.

How to Search US Patents

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There are 2 databases you should try for searching US Patents and US Patent Application Publications.  The US Patent & Trademark Office (PTO) databases cover US issued patents and US patent application publications and are free of charge.  The Delphion web site has access to patent documents or abstracts from the US, Japan, PCT (Patent Cooperation Treaty), EPO (European Patent Office), and the INPADOC collection, which covers 71 patent offices worldwide.  However, in order to use all of these features you need a paid subscription, which is at least $75 per month.  With a free, basic registration, you can do "quick" searches in granted US patents and publication number searches in the entire Delphion collection.

If you do not want to spend money, I suggest that you use the US PTO databases since the Delphion "quick" search is inadequate.

Even if you are interested in searching non-US patent documents, you should generally start by searching the US collection.  The US collection, with almost 6.6 million issued patents, is the largest patent collection in the world.

The US is also the world's largest economy.  Therefore, non-US companies seek US patents for inventions that they consider to be the most important strategically for their business.

In the past, one reason for preferring searches of non-US collections was the problem of timeliness: US patent applications were kept confidential by the USPTO until the patent was granted (typically 2 to 3 years after filing) while the PCT, EPO, and Japan patent applications are published 18 months after filing.  However, the US has made a major change in its patent policy to harmonize with the other countries.  With some exceptions, all US patent applications filed on or after November 29, 2000 are published after 18 months. 

Go to the USPTO databases.  Notice that the granted patents and patent application publications are kept in separate databases.  This means that you have to search in each one if you want to search all US patent documents.  One advantage of Delphion is that both US collections can be searched simultaneously.

Doing a bad patent search is easy but doing a good patent search is hard.

Step 1: Search by Key Words, Inventor Names, Assignee Names, etc.

Suppose that you are looking for patents in the area of gallium nitride light-emitting diodes (LEDs).  The patents may actually have titles such as  "Semiconductor Device," "Optical Device," "Light Emitting Device," "Group III-Nitride Light Emitting Device," and so on.

"Semiconductor Device": Titles like these are very common and may include not only gallium nitride but any of the other semiconductors such as Si, GaAs, InP, and perhaps even the semiconducting polymers.  The devices could be lasers, LEDs, shift registers, etc.

"Optical Device": Again titles like these are common and could be for LEDs, but could also be for liquid crystal displays, lasers, deformable micromirror devices, etc. 

"Light Emitting Device": This is also not helpful.  The patent could be for lamps, lasers, light emitting diodes, etc.  The light emitting material is also not specified: GaAs, GaN, polymers, organic molecules, phosphors?

"Group III-Nitride Light Emitting Device": This title appears to be the most helpful to the search but still does not contain the 2 key words that were originally envisioned: "gallium nitride" and "light emitting diode".

Therefore you should start out by searching numerous combinations of all the key words you can think of on not only the titles but also the abstract, claim(s), and description/specification fields.  You will not get all of the documents you seek and you will get documents other than the one you want, but this is a start.  Scan the abstracts of these documents to select the ones that appear to be relevant to you.

If you are familiar with the subject matter and know the inventor name or the assignee name, you can use these to narrow the search.  However, in the case of the patent application publication collection, you must be careful.  Many of these documents do not show the assignee name.

If the assignee is a small start-up company, you may be able to simply search by the assignee name and find a small number of documents that you can easily read.  However, there are some pitfalls.  The start-up may be too young to have any issued patents and its patent applications publications may not have the assignee name on them.  The start-up may have started by spinning off or licensing from somebody else.  Therefore, the assignee of the patent you are seeking may be "Regents of the University of Slobovia" rather than "Startup, Inc."

Step 2: Follow the Forward and Backward References

A very important step is to look at the forward and backward references of the documents you selected in Step 1.  You should not skip this steps because this is work that the patent examiners have already done for you.

Forward references of patent A are those patents that reference A as prior art.  Similarly, backward references of patent A are those documents that A references as prior art.  You should take full advantage of these references (e.g. forward references of forward references, backward references of forward references) to start building a collection of relevant patent documents.

This approach is effective for issued patents but does not work too well for patent application publications.  The patent application publications have not yet been examined and do not have forward and backward references in a readily accessible format.

Step 3: Search by US Classification Code

Once you have some good hits, take a look at the US Classification Code (Field 52) on the first page of the patent document.  If you look at the classification codes of your relevant hits, you should notice some codes that appear repeatedly.  The US PTO web site has a database of classification codes.

All patents are classified into a class/subclass.  Some subclasses are indented under other subclasses.  You may want to read the class/subclass descriptions to try to find the one that best describes your target.  Once you find several class/subclasses, you can do a classification code search of multiple class/subclasses with the Boolean operator AND to refine the search.  Of course you can combine with other search fields such as inventor name, assignee name, range of issue dates, etc.

The next chapter is How to Read US Patents.