global class deleteCampaignMembers implements Database.Batchable<sObject>
{
    global String Query;
    global void deleteCampaignMembers()
    {
        Query='select id from campaignMember where createdDate > LAST_90_DAYS';
    }

    global Database.QueryLocator start(Database.BatchableContext BC)
    {
        return Database.getQueryLocator(query);
    }

    global void execute(Database.BatchableContext BC,List<sObject> scope)
    {
        Delete scope;
    }

    global void finish(Database.BatchableContext BC)
    {
        //Send an email to the User after your batch completes
        Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
        String[] toAddresses = new String[] {'dllewellyn@foodperspectives.com'};
        mail.setToAddresses(toAddresses);
        mail.setSubject('Apex Batch Job is done');
        mail.setPlainTextBody('The batch Apex job processed ');
        Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
    }
}