CMUT device and imaging method
A capacitive micro-machined ultrasonic transducer, CMUT, device in which integrated probe circuitry includes both the ultrasound transmission and reception circuitry and a DC-DC converter for generating a bias voltage for the CMUT cell. The high voltage pulses of a pulser circuit and a high voltage DC bias voltage are both generated by a single probe circuit, which is local to the CMUT cell.
1 . An ultrasound imaging method, comprising:
using an application specific integrated circuit (ASIC) that comprises a DC-DC converter and transmit-and-receive circuitry and that is physically and electrically connected to a three-electrode capacitive micro-machined ultrasound transducer (CMUT) cell, to:
perform ultrasound data acquisition including using the transmit-and-receive circuitry to generate ultrasound transmission pulses and to detect ultrasound echo signals; and
generate a bias voltage for the three-electrode CMUT cell using the DC-DC converter,
wherein the three-electrode CMUT cell comprises a first electrode coupled to a cell membrane, a second electrode embedded into a cell floor opposing the first electrode and separated therefrom by a gas or vacuum cavity, and a third electrode which is capacitively coupled with the first or second electrode;
wherein the generated bias voltage is provided to the third electrode of the three-electrode CMUT cell, and wherein the ultrasound transmission pulses are generated by applying an alternating current (AC) voltage over the second and first electrodes;
wherein the method further comprises using a timing scheme for alternated operation in which the ultrasound data acquisition is alternated with operation of the DC-DC converter.
2 . The method as claimed in claim 1 , wherein, during the ultrasound data acquisition, a clock of the DC-DC converter is switched off, and wherein, during the operation of the DC-DC converter, the DC-DC converter is switched in dependence of said clock for generating the bias voltage.
3 . The method as claimed in claim 2 , further comprising storing the generated bias voltage on a decoupling capacitor that is connected to the third electrode during the operation of the DC-DC converter, and maintaining said generated bias voltage during the ultrasound data acquisition.
4 . A capacitive micro-machined ultrasound transducer (CMUT) device, comprising:
a CMUT cell comprising a first electrode coupled to a cell membrane, a second electrode embedded into a cell floor opposing the first electrode and separated therefrom by a gas or vacuum cavity, and a third electrode which is capacitively coupled with the first or second electrode;
an application specific integrated circuit (ASIC) that is physically and electrically connected to the CMUT cell, wherein the ASIC comprises:
a DC-DC converter to generate a bias voltage for the three-electrode CMUT cell; and
transmit-and-receive circuitry to perform ultrasound data acquisition including using the transmit-and-receive circuitry to generate ultrasound transmission pulses and to detect ultrasound echo signals, wherein the ultrasound transmission pulses are generated by applying an alternating current (AC) voltage over the second and first electrodes;
wherein the DC-DC converter and the transmit-and-receive circuitry are configured to be controlled by a controller using a timing scheme for alternated operation in which the ultrasound data acquisition is alternated with operation of the DC-DC converter.
5 . The device as claimed in claim 4 , wherein the bias voltage generated by the DC-DC converter is in a range of about 50V to about 120V.
6 . The device as claimed in claim 4 , wherein the DC-DC converter comprises a switched capacitor converter.
7 . The device as claimed in claim 4 , wherein the device is configured such that during the ultrasound data acquisition, a clock of the DC-DC converter is switched off, and such that during the operation of the DC-DC converter, the DC-DC converter is switched in dependence of said clock for generating the bias voltage.
8 . The device as claimed in claim 4 , wherein the CMUT cell and the ASIC are monolithically integrated.
9 . The device as claimed in claim 4 , wherein the CMUT cell comprises a substrate and a dielectric layer, wherein the second electrode is deposited onto the substrate opposing the third electrode on a side opposite to the cavity, wherein the third electrode is located in between the first electrode and the second electrode;
wherein the dielectric layer is in direct contact with and sandwiched between the second and third electrodes.
10 . The device as claimed in claim 9 , wherein the substrate is coupled to a top surface of the ASIC.
11 . The device as claimed in claim 10 , further comprising an insulator providing an insulating function for the second electrode towards electronics of the ASIC, wherein a distance between the second electrode and the top surface of the ASIC corresponds to a thickness of the insulator.
12 . The device as claimed in claim 11 , wherein the insulator is a buried oxide.
13 . The device as claimed in claim 9 , wherein a capacitance between the first electrode and the third electrode is much smaller than a capacitance between the third electrode and the second electrode.
14 . The device as claimed in claim 13 , further comprising a decoupling capacitor that is connected to the third electrode and that is configured for storing the generated bias voltage.
15 . The device as claimed in claim 14 , wherein the decoupling capacitor is an on-chip capacitor that is comprised by the ASIC.
16 . An ultrasound imaging system comprising the CMUT device of claim 4 , and comprising the controller for controlling the DC-DC converter and the transmit-and-receive circuitry using the timing scheme for alternated operation in which the ultrasound data acquisition is alternated with operation of the DC-DC converter.