An alternative approach to the manufacture of varactors is to realise them using micro-system technology, also designated as Micro-Electro-Mechanical Systems, abbreviated as MEMS.  A MEMS part is a miniaturised part of which the components provide dimensions in the micrometer range.  The individual components work together as a system. 
MEMS-based varactors provide a metallic membrane which is mounted in a movable manner above an actuator electrode.  If a direct voltage is applied between the actuator electrode and the metallic membrane, the electrostatic forces of the actuator cause a displacement of the membrane.  A variation in the potential of the direct voltage changes the distance between actuator electrode and metallic membrane.  The actuator electrode and the metallic membrane represent a plate capacitor from which a capacitance value can be tapped. 
Because of the variable distance between the membrane and the actuator, the capacitance value is variable.  Such tunable capacitors are used, for example, in Voltage Controlled Oscillators VCO (Voltage Controlled Oscillators) in order to adjust the oscillation frequency. 
Such a varactor is described in WO 2004/038848 A2.  In this context, a movable membrane is arranged between two substrate layers.  A varactor with high-quality and a broad tuning range can be manufactured through embodiment with two substrate layers. 
MEMS-based varactors provide a high sensitivity to mechanical vibrations, oscillations and accelerations.  As a result of the mechanical mode of operation, accelerations on the varactor influence the adjusted capacitance value.  Because of this property, MEMS-varactors are also used as acceleration sensors. 
This sensitivity to acceleration is disadvantageous if the varactor is supposed to provide an adjustable but constant capacitance value, for example, for applications in information technology and high-frequency technology. 
An object of the present invention is therefore to provide a varactor and a varactor system which provides an adjustable but stable capacitance value.  In particular, the varactor should be embodied to be resistant to influences based on an acceleration of the varactor.