How to show year and month only in Date Field for specific entities?

[sujithraalink]

How to show Year and Month only in a field for specific entity? I have an entity called certificate , and in this entity i have a date field called "passoutyear". In this field i have to show year and month only..dont want date. How can i achieve this? or should i use another field type. If so How can i achieve this? please help me.