Memory devices
A passive memory device includes a plurality of resonant members, e.g. of a cantilever or bridge-type form, that may have different resonant frequencies and that may be held against vibrations by end or side tethers. Data may be recorded in the device by removing various of the tethers, so that, on applying an excitation signal, e.g. from a transmitter, untethered resonant members vibrate strongly in response to their resonant frequencies, and provide a response signal that can be picked up e.g. by a receiver and correlated with the excitation signal frequencies to determine which resonant members have been untethered. The response by an untethered resonant member can correspond to a logical “1”, whilst the lack of a response signal at a known resonant member frequency can correspond to a logical “0”, or vice versa. The device may be made using MEMS technology, and various device structures and excitation/detection methods are disclosed including the use of excitation/detection circuitry within the device and the use of magnetic, Lorentz, electrostatic and/or piezoelectric forces.
1. A memory device including an array of bridge-type resonant members adapted to vibrate in response to an applied Lorentz force in order to represent data, wherein a common electrical conductor extends along the lengths of a plurality of resonant members in the array and forms part of excitation circuitry for coupling with an applied excitation signal and causing vibration of the resonant members.
2. The memory device of claim 1 , wherein the resonant members are held against vibration by restraining elements, disablement of the restraining elements allowing associated resonant members to vibrate in response to an applied Lorentz force.
3. The memory device of claim 2 , wherein the restraining elements are provided at the sides of the resonant members.
4. The memory device of claim 3 , wherein the restraining elements are fusible, and wherein the device includes fusing circuitry for passing a fusing current through the fusible restraining elements, the fusing circuitry including an addressable array for fusing individual restraining elements.
5. The memory device of claim 3 , wherein the restraining elements are configured to be removable by ablation.
6. A method of recording data on a memory device according to claim 2 , the method comprising disabling restraining elements in the memory device in accordance with the data to be recorded.
7. The memory device of claim 1 , wherein the resonant members have different resonant frequencies from one another.
8. The memory device of claim 1 , including detection circuitry associated with resonant members, such that a characteristic of the circuitry is changed due to vibration of the resonant members.
9. The memory device of claim 1 , wherein the electrical conductor takes a serpentine form.
10. The memory device of claim 1 , wherein the memory device is fabricated using MEMS technology.
11. The memory device of claim 1 , wherein the resonant members are formed on a dielectric or semiconductor substrate.
12. The memory device of claim 11 , wherein the excitation circuitry is fabricated on the same dielectric or semiconductor substrate.
13. An RFID device including the memory device of claim 1 .
14. A data storage system including the memory device of claim 1 , and an interrogator including a signal generator for applying an interrogation signal to the device and a receiver for receiving a response to the interrogation signal and for analysing the signal in order to determine which of the resonant members in the device vibrate.
15. The data storage system of claim 14 , wherein the interrogation signal induces an alternating current in the electrical conductor, and wherein a magnetic element is provided in the memory device to provide a magnetic field across the resonant members orthogonal to the direction of current flow.
16. The data storage system of claim 14 , wherein the interrogation signal induces an alternating current in the electrical conductor, and wherein the interrogator applies a magnetic field across the resonant members orthogonal to the direction of current flow.
17. The memory device of claim 1 , wherein the excitation signal induces an alternating current in the electrical conductor.
18. The memory device of claim 17 , wherein the excitation circuitry includes an antenna circuit, the alternating current being induced in the antenna circuit.
19. The memory device of claim 18 , wherein the antenna circuit includes a coil.
20. The memory device of claim 19 , wherein the resonant members change impedance when resonating based on vibration of the associated resonant members.
21. The memory device of claim 19 , wherein the excitation circuitry, including the coil, and the resonant members are fabricated on the same substrate.
22. The memory device of claim 1 , including a permanent magnetic element for providing a magnetic field across the resonant members.
23. A method of reading data recorded on the memory device of claim 1 , including the steps of:
applying an interrogation signal to the memory device so as to cause the associated resonant members to vibrate,
receiving a response to the interrogation signal, and
analysing the response in order to determine which of the resonant members in the device vibrate.
24. The method of reading data of claim 23 , wherein the interrogation signal induces an alternating current in the electrical conductor, and wherein a magnetic element is provided in the memory device to provide a magnetic field across the resonant members orthogonal to the direction of current flow.
25. The method of reading data of claim 24 , wherein the magnetic field is applied by an external field applied at the same time as the interrogation signal.
26. The method of reading data of claim 23 , wherein the interrogation signal induces an alternating current in the electrical conductor, and wherein the step of applying an interrogation signal to the memory device includes applying a magnetic field across the resonant members orthogonal to the direction of current flow.
27. The memory device of claim 3 , in which a plurality of restraining elements have been disabled, so as to encode the device with data.