Manuel Dominguez-Pumar

Delta-sigma control of dielectric charge for contactless capacitive MEMS

In this paper, we present a new closed-loop control method of dielectric charge for contactless capacitive microelectromechanical systems. The method uses a feedback loop to maintain the net charge in the dielectric layer at the desired level. We show that, under particular conditions, the control loop is similar to a thermal sigma-delta modulator as used in thermal sensors. In this way, the control actuation will inject an average charge into the dielectric to keep it at a desired level while applying an actuation bit stream to compensate the charge being continuously leaked out of the dielectric. The validation of the method is carried out employing numerical simulation and experimental measurements of Poly-MUMPS devices.

Dielectric Charge Control in Electrostatic MEMS Positioners/Varactors

A new dynamical closed-loop method is proposed to control dielectric charging in capacitive microelectromechanical systems (MEMS) positioners/varactors for enhanced reliability and robustness. Instead of adjusting the magnitude of the control voltage to compensate the drift caused by the dielectric charge, the method uses a feedback loop to maintain it at a desired level: the device capacitance is periodically sampled, and bipolar pulses of constant magnitude are applied. Specific models describing the dynamics of charge and a control map are introduced. Validation of the proposed method is accomplished both through discrete-time simulations and with experiments using MEMS devices that suffer from dielectric charging.

Sliding-Mode Analysis of the Dynamics of Sigma-Delta Controls of Dielectric Charging

The purpose of this paper is to show that sigma-delta controllers of dielectric charge can be analyzed using the tools of sliding-mode controllers, in the infinite sampling frequency approximation. This allows to study the dynamics of the hidden state variables related to the charge in the dielectric, as well as the reachability and stability of the control method. Furthermore, it is also possible to explain the response of the control bitstream as a function of the dynamical model of the system. This approach not only provides insight into the dynamics of the charge controllers, understood as hybrid systems, it also simplifies the modeling and simulations of the system.

Spherical Wind Sensor for the Atmosphere of Mars

A novel wind speed and direction sensor designed for the atmosphere of Mars is described. It is based on a spherical shell divided into four triangular sectors according to the central projection of tetrahedron onto the surface of the unit sphere. Each sector is individually controlled to be heated above the ambient temperature independently of the wind velocity and incidence angle. A convection heat rate model of four hot spherical triangles under forced wind has been built with finite element method thermal-fluidic simulations. The angular sensitivity of the tetrahedral sphere structure has been theoretically determined and compared with the tessellation of the sphere by four biangles. A 9-mm-diameter prototype has been assembled using 3-D printing of the spherical shell housing in the interior commercial platinum resistors connected to an extension of a custom design printed board. Measurements in Martian-like atmosphere demonstrate sensor responsiveness to the flow in the velocity range 1-13 m/s at 10-mBar CO2 pressure. Numerical modelization of the sensor behavior allows to devise an inverse algorithm to retrieve the wind direction data from the raw measurements of the power delivered to each spherical sector. The functionality of the inverse algorithm is also demonstrated.

Heat Flow Dynamics in Thermal Systems Described by Diffusive Representation

The objective of this paper is to analyze the dynamics of heat flow in thermal structures working under constant temperature operation. This analysis is made using the tools of sliding mode controllers. The theory is developed considering that the thermal system can be described using diffusive representation. The experimental corroboration has been made with a prototype of a wind sensor for Mars atmosphere being controlled by a thermal sigma-delta modulator. This sensor structure allows to analyze the time-varying case experimentally since changes in wind conditions imply changes in the corresponding thermal models. The diffusive symbols of the experimental structures have been obtained from open-loop measurements in which pseudorandom binary sequences of heat are injected in the sensor. With the proposed approach, it is possible to predict heat flux transient waveforms in systems described by any arbitrary number of poles. This allows for the first time the analysis of lumped and distributed systems without any limitation on the number of poles describing it.

Closed-Loop Compensation of Dielectric Charge Induced by Ionizing Radiation

This letter investigates the capability of dielectric charge control loops to cope with charge induced by ionizing radiation. To this effect, an microelectromechanical systems (MEMS) variable capacitor has been irradiated with X-rays and gamma-radiation in three scenarios: without polarization; using an open-loop dielectric charge mitigation strategy; and using a closed-loop control method. The results show that the charge effects induced by radiation can be partially compensated using dielectric charge control.

Charge Trapping Control in MOS Capacitors

This paper presents an active control of capacitance–voltage (C–V) characteristic for MOS capacitors based on sliding-mode control and sigma–delta modulation. The capacitance of the device at a certain voltage is measured periodically and adequate voltage excitations are generated by a feedback loop to place the C–V curve at the desired target position. Experimental results are presented for an n-type c-Si MOS capacitor made with silicon dioxide. It is shown that with this approach, it is possible to shift the C–V curve horizontally to the desired operation point. A physical analysis is also presented to explain how the C–V horizontal displacements can be linked to charge trapping in the bulk of the oxide and/or in the silicon–oxide interface. Finally, design criteria are provided for tuning the main parameters of the sliding-mode controller.

Active Control of the Surface Potential of Nanostructured Layers

The objective of this letter is to show the first results obtained with a control designed to keep the average surface potential of a nanostructured layerconstant. This condition is equivalent to keeping constant the resistivity of the layer measured at a constant reference temperature. The proposed closed-loop control achieves this objective by adequately changing the average temperature of the temperature waveforms applied to the nanostructured layer. Experiments are shown on which the control is applied to a layer made of Au-functionalized WO3 nanoneedles.

Low pressure spherical thermal anemometer for space missions

A novel spherically shaped thermal anemometer for low pressure, Mars-like conditions, is described. The concept has been designed using finite element multyphysics simulations to find out the thermal conductance to the ambient for varying conditions of wind speed and direction and ambient pressure and temperature. A prototype 1cm diameter suitable to work under these environment in the range 0.25-10m/s speed has been build using 3D printing and tested inside a low pressure chamber. The protopype shown has two separated hemispheres, independently heated above the ambient temperature, providing angle sensitivity in one plane. Measurements of the heating power in both hemispheres required to keep an overheat of 30K are shown as a function of the wind direction showing good sensitivity at 0.5m/s. One improvement of this sensor is the means provided to also heat the core of the sphere where the circuit board is located thereby avoiding most of the conduction losses to the supports. The concept is scalable to other wind speed and pressure conditions and also to full 3D measurements.

Closed-Loop Compensation of Charge Trapping Induced by Ionizing Radiation in MOS Capacitors

The objective of this paper is to explore the capability of a charge trapping control loop to continuously compensate charge induced by ionizing radiation in the dielectric of metal–oxide–semiconductor (MOS) capacitors. To this effect, two devices made with silicon oxide have been simultaneously irradiated with gamma radiation: one with constant voltage bias and the other working under a dielectric charge control. The experiment shows substantial charge trapping in the uncontrolled device, whereas, at the same time, the control loop is able to compensate the charge induced by gamma radiation in the second device.