Create the value object that you want to use as your custom type.
In my case the file module/Geo/src/Domain/Address/Id.php
Create the doctrine type class.
In my case in module/Geo/src/Doctrine/Type/
Setup the configuration for doctrine in the ConfigProvider class of your module.
In my case module/Geo/src/ConfigProvider.php
Use your type in a doctrine entity.
In my case in the file module/Geo/src/Domain/Address.php