Technically, Tier IV is still PERS. It simply is a defined contribution plan rather than a defined benefit. 

The employee contributes. The employer's contribution stays with the system at a rate declining from 75% after the 2nd year of employment to 25% at year 4 if the employee leaves with less than 5 years. IOW, at year 2, an employee leaving the system can pull all of their contributions, plus 25% of the employer's. At year 3, again, all of their contribution plus 50% of all contributions made by the employer. At year 4, again, all employee contributions, plus 75% of all the employer's contributions.