I don't understand the term "custom micro RFID." Broadly speaking, there are two different types of customization for RFID tags.
You can customize a tag antenna for a specific application. This might mean having a tag designed with an antenna that would provide the best performance within a certain size constraint or shape requirement. Or it might mean matching the antenna's impedance to the material on which the tag will be placed, in order to obtain optimal performance. Most tag companies, such as Avery Dennison, Invengo and Smartrac, offer design services. Prototypes can be created quickly and tested before a batch of tags is produced.
There is also customization involving the protective housing and/or attachment method for a standard transponder. For example, you might require a tag that could withstand having a bowling ball dropped on it, or that could be attached to a telephone pole with nails or an engine block via epoxy. There are several companies, such as HID Global, William Frick & Co. and Xerafy, that will develop custom tags for virtually any application.
If this is not what you are looking for, please resubmit your question and explain what you mean by "custom micro RFID."
—Mark Roberti, Founder and Editor, RFID Journal