Searching for parameter value in a postgres column

I'm attempting to implement an advanced search on my Rails 5 site. The user passes in a parameter "provider_type", and I would like to return all records that contain that value. The value is chosen from a dropdown list using simple-form. My new.html.erb looks like this:

<%= simple_form_for Search.new, :html => {:class => 'form-horizontal' } do |f| %>
    <%= f.input :provider_type, collection: ['Mental Health', 'Medical'] %>
    <%= f.button :submit %>
<% end %>

My Search model looks like this:

class Search < ApplicationRecord
    def search_providers
        providers = Provider.all
        providers = providers.where("provider_type LIKE ?", ['Mental Health', 'Medical']) if provider_type.present?
        providers
    end
end

And my Searches controller:

def SearchesController < ApplicationController
    def new
        @types = Provider.uniq.pluck(:provider_type)
    end

    private
        def search_params
            params.require(:search).permit(:provider_type)
        end
    end
end

When I try to search for 'Mental Health' in the search form, I get this error: PG::UndefinedFunction: ERROR: operator does not exist: character varying[] ~~ unknown

EDIT

When I reword it as

providers.where(provider_type: provider_type) if provider_type.present?

This produces the error "PG::InvalidTextRepresentation: ERROR: malformed array literal: "%Mental Health%" DETAIL: Array value mut start with "{" or dimension information.