According to the Library of Congress guide to cataloging, a massive 5-volume set of all approved subjects:
For Memoirs, use the subject heading "Personal Memoirs" in conjunction with an individual, topic, or event.
Do NOT limit the publication date, as you may exclude reprints.
You can also use the Subject term Autobiograph* in worldcat and the catalog, but it doesn't work well. Many catalogers, for reason beyond my understanding, often use Autobiography and biography interchangeably, and in fact there is a subject heading called BIOGRAPHY & AUTOBIOGRAPHY
The best way to find a specific autobiography is to search autobiography as a title term, combined with the individuals make as a keyword.
The best way to find memoirs and autobiographies is using the methods above, however we do have some databases that may include memoirs.