I am afraid you do need one. The document check list in the citizenship website clearly indicate that :
........You will need to provide original penal clearance certificates from overseas countries if, since the grant of your permanent Australian visa:
you lived or travelled overseas since the age of 18 years or over, and
the total time spent overseas added up to 12 months or more, and
the time spent in any one country was more than 90 days, or
you are requested to do so by the department.