Android :: Using Cache Or SDcard As Temporary Buffer

I'm currently trying to create a buffer for my application which needs to be big!I mean at least 1MB but most likely to be 4MB.Now definitely bad idea to actually allocate this much on a byte array in memory.So the options are put all the data in a file. So question is where do I place this temp file?

Option 1: Store to sdcard. Might be slow and not such a good idea for continuous read/writes?

Option 2: Store to in the apps cache.I read somewhere this is fast for read/ writes. But also read before issues cleaning up the cache after use? I guess I should as if I be able to create a file in cache and discard it when I don't need it? Any tips/look outs from using this methods would be greatly appreciated!