Some Han characters are ideographic in nature, but not all of them. Korean used to be written with Han characters (using sets of very complicated rules for how to apply them to the language) prior to the invention of Hangeul, but other than a handful of them they aren't in widespread use any more outside specialized or educational contexts. However, some of the Hangeul letters are featural in design, e.g. the velar consonant ㄱ (g/k) is meant to be a side view of the tongue when producing its sound.