A Second-Order Delta-Sigma Control of Dielectric Charge for Contactless Capacitive MEMS

Abstract

Abstract-This letter introduces a new second-order deltasigma method for control of the dielectric charge in contactless capacitive MEMS. This method improves one previously proposed by the authors, providing second-order quantization noise shaping and allowing to avoid the plateaus typical of first-order strategies. The feasibility and the features of the new method are demonstrated both experimentally and through simulations.

Closed-Loop Compensation of Dielectric Charge Induced by Ionizing Radiation

“…Closed-loop methods to control the amount of actuation-induced net dielectric charge have been demonstrated in [1]- [4]. Ionizing radiation can also induce dielectric charge in MEMS devices operating in space or harsh environments [5]- [7].…”

Charge induced by ionizing radiation understood as a disturbance in a sliding mode control of dielectric charge

“…In the rest state (zero voltage applied and zero net charge trapped in the dielectric), the air gap between the moveable plate and the dielectric is 2.75µm and the pull-in voltage is 24V. This device, fabricated with standard PolyMUMPS technology, is from the same batch as the ones used in [14], [15].…”

“…The block diagram shown in Figure 1 describes the secondorder sigma-delta control of dielectric charge proposed in [15] and used in this work. It is a sampled-time circuit in which only two voltage values, V + >0 and V − <0, are used to actuate the device.…”

“…In the sigma-delta controls proposed in [14] and [15], the dielectric is seen as a leaky charge integrator working under two competing mechanisms: charge being injected by the actuation waveforms BIT0 and BIT1 and charge escaping the traps in the material. The sigma-delta loops generate sequences of BIT0 and BIT1 waveforms (output bitstream) that compensate in average the charge being leaked out of the dielectric, thus allowing to reach and maintain a given value of total dielectric charge Q n = Q target .…”

“…The main drawback of these strategies is that they cannot guarantee long-term stability since they cannot adapt to drifts of the charging characteristics of the dielectric layers. In view of this, a family of sigma-delta closed-loop controls has been proposed recently, [13]- [15]. These controls generate adequate sequences of bipolar actuation voltages to keep constant at the desired level the total charge in the dielectric, or what is the same the voltage shift of the of capacitance-voltage, C-V , curve of the device.…”