You need to use a plugin for that. You can use a plugin like JIRA Misc Custom Fields and use the "write it" option or you can create a custom plugin.
JIRA Misc Custom Field - https://marketplace.atlassian.com/plugins/com.innovalog.jmcf.jira-misc-custom-fields
Create a custom plugin - https://confluence.atlassian.com/display/JIRA041/How+to+create+a+new+Custom+Field+Type#
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