Methods of forming planar carbon nanotube ("CNT") resistivity-switching materials for use in memory cells are provided, that include depositing first dielectric material, patterning the first dielectric material, etching the first dielectric material to form a feature within the first dielectric material, depositing CNT resistivity-switching material over the first dielectric material to fill the feature at least partially with the CNT resistivity-switching material, depositing second dielectric material over the CNT resistivity-switching material, and planarizing the second dielectric material and the CNT resistivity-switching material so as to expose at least a portion of the CNT resistivity-switching material within the feature. Other aspects are also provided.