1. A pressure sensor comprising:
a diaphragm and a sidewall, the sidewall having an interior side defining a backside cavity, the backside cavity extending from a portion of an insulator layer directly in contact with the diaphragm to a backside opening,
wherein the interior side of the sidewall is formed using a deep reactive ion etch and is substantially orthogonal to the diaphragm,
wherein the deep reactive ion etch begins at the backside opening and etches towards the diaphragm at a rate that is substantially reduced when the insulator layer is reached, and
wherein the backside opening is non-rectangular.
2. The pressure sensor of claim 1 wherein the backside opening forms a rounded square.
3. The pressure sensor of claim 1 wherein the backside opening is shaped as a castle.
4. An absolute pressure sensor comprising:
a first silicon layer comprising a diaphragm having a top and a bottom;
an insulator layer covering the bottom of the diaphragm; and
a second silicon layer below the insulator layer and comprising a sidewall extending from the insulator layer on the bottom of the diaphragm, the sidewall having an interior side forming a backside cavity having a backside opening, the interior side substantially orthogonal to the diaphragm; and
a block covering the backside opening such that a hermetic seal is formed.
5. The absolute pressure sensor of claim 4 wherein the block is silicon.
6. The absolute pressure sensor of claim 4 wherein the block is glass.
7. An absolute pressure sensor comprising:
a diaphragm having a top and a bottom;
a sidewall extending from the bottom of the diaphragm, the sidewall having an interior side forming a backside cavity having a backside opening, the interior side substantially orthogonal to the diaphragm; and
a block covering the backside opening such that a hermetic seal is formed,
wherein the block is glass, and
wherein the glass block is covered with metal over the backside opening.
8. A silicon wafer comprising:
a plurality of pressure sensors, each pressure sensor comprising:
a diaphragm having a top and a bottom; and
a sidewall extending from the bottom of the diaphragm, the sidewall having an interior side formed using a deep reactive ion etch and forming a backside cavity having a backside opening, the interior side substantially orthogonal to the diaphragm,
wherein the plurality of pressure sensors includes approximately at least twenty-thousand pressure sensors,
and wherein the silicon wafer is a 150 mm (6 inch) wafer.
9. A pressure sensor apparatus comprising:
exactly one pressure sensor in a housing, the exactly one pressure sensor comprising:
a diaphragm having a top and a bottom; and
a sidewall extending from the bottom of the diaphragm, the sidewall having an interior side formed using a deep reactive ion etch and forming a backside cavity having a backside opening, the interior side substantially orthogonal to the diaphragm,
wherein the diaphragm is less than 350 microns in length, and
the diaphragm accounts for more than 10 percent of an area of the exactly one pressure sensor.
10. A pressure sensor comprising:
a diaphragm having a top and a bottom;
a sidewall extending from the bottom of the diaphragm, the sidewall having an interior side forming a backside cavity having a backside opening, the interior side substantially orthogonal to the diaphragm;
a cap attached to the top of the diaphragm;
a first electrode attached to the top of the diaphragm; and
a second electrode attached to an underside of the cap,
wherein the cap and diaphragm form a reference cavity, and
wherein the first electrode and the second electrode form a capacitor.
11. A pressure sensor comprising:
a diaphragm having a top and a bottom;
a sidewall extending from the bottom of the diaphragm, the sidewall having an interior side forming a backside cavity having a backside opening, the interior side substantially orthogonal to the diaphragm;
a cap attached to the top of the diaphragm;
a plurality of resistors in the top of the diaphragm,
wherein the cap and diaphragm form a reference cavity, and
wherein the plurality of resistors form a piezoresistive sensing circuit.
12. A pressure sensor comprising:
a first silicon layer comprising a diaphragm;
an insulator layer below the first silicon layer;
a second silicon layer below the insulator layer and having a backside cavity defined by a sidewall, a backside opening, and a portion of the insulator layer below and directly in contact with the diaphragm,
wherein the backside cavity is formed using a deep reactive ion etch and the sidewall is substantially orthogonal to the diaphragm,
wherein the backside opening is non-rectangular.
13. The pressure sensor of claim 12 wherein the backside opening forms a rounded square.
14. The pressure sensor of claim 12 wherein the backside opening is shaped as a castle.
15. The pressure sensor of claim 12 further comprising:
a block covering the backside opening such that a hermetic seal is formed.
16. The pressure sensor of claim 15 wherein the block is silicon.
17. The pressure sensor of claim 15 wherein the block is glass.
18. The pressure sensor of claim 17 wherein the glass block is covered with metal over the backside opening.
19. A pressure sensor comprising:
a first silicon layer having a top side and a bottom side and comprising a diaphragm;
an insulator layer having a top side and a bottom side, the top side in contact with the bottom side of the first silicon layer;
a second silicon layer having a top side and a bottom side, the top side in contact with the bottom side of the insulator layer and having a backside cavity defined by a sidewall, a portion of the bottom side of the insulator layer, and a backside opening in the bottom side of the second silicon layer,
wherein the backside cavity is formed using a deep reactive ion etch and the sidewall is substantially orthogonal to the diaphragm.
20. The pressure sensor of claim 19 wherein the backside opening forms a rounded square.
21. The pressure sensor of claim 19 wherein the backside opening is shaped as a castle.
22. The pressure sensor of claim 19 further comprising:
a block covering the backside opening such that a hermetic seal is formed.
23. The pressure sensor of claim 22 wherein the block is silicon.
24. The pressure sensor of claim 22 wherein the block is glass.
25. The pressure sensor of claim 24 wherein the glass block is covered with metal over the backside opening.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An interface circuit that relays a signal between a first external circuit and a second external circuit selectively using a single-ended transmission system and a differential transmission system, the interface circuit comprising:
a signal reception unit operable to receive, from the first external circuit, a system signal indicating either of the single-ended transmission system and the differential transmission system;
an input control circuit operable, (i) when the system signal indicates the single-ended transmission system, to receive a first data signal and a second data signal from the first external circuit, and to output the first data signal and the second data signal as a first input signal and a second input signal, respectively, and (ii) when the system signal indicates the differential transmission system, to receive a third data signal from the first external circuit, and to output the third data signal and an inverted logic signal of the third data signal as the first and the second input signals, respectively;
a first driver circuit operable to receive the first input signal, to generate a first output signal based on the received first input signal, and to output the first output signal to the second external circuit;
a second driver circuit operable to receive the second input signal, to generate a second output signal based on the received second input signal, and to output the second output signal to the second external circuit; and
a drive control circuit operable to select a constant-voltage driving system or a constant-current driving system according to the system signal, and to control, according to the selection, voltage and current that are supplied from a power supply to the first and the second driver circuits, wherein
the first driver circuit switches between conduction and non-conduction states of the current supplied from the power supply according to a level of the first input signal so as to generate the first output signal,
the second driver circuit switches between conduction and non-conduction states of the current according to a level of the second input signal so as to generate the second output signal,
the signal reception unit further receives, from the first external circuit, a direction signal indicating a transmission direction, and
the interface circuit further comprises:
a first signal line and a second signal line operable to establish connections between the first driver circuit and the second external circuit and between the second driver circuit and the second external circuit, respectively;
an output control circuit operable to receive the first and the second input signals from the input control circuit, and (i) when the direction signal indicates the transmission direction from the first external circuit to the second external circuit, to output the first and the second input signals to the first and the second driver circuits, respectively, (ii) when the direction signal indicates the transmission direction from the second external circuit to the first external circuit, to disconnect the input control circuit from the second external circuit;
a termination resistance circuit connected at one end to the first signal line and at another end to the second signal line, the termination resistance circuit having a given resistance value;
a differential receiver circuit operable to receive differential signals from the second external circuit via the first and the second signal lines;
a first single-ended receiver circuit operable to receive a single-ended signal from the second external circuit via the first signal line; and
a second single-ended receiver circuit operable to receive a single-ended signal from the second external circuit via the second signal line.
2. The interface circuit of claim 1, further comprising:
a receiver switch circuit operable, when the direction signal indicates the transmission direction from the second external circuit to the first external circuit, to establish a connection between the drive control circuit and the differential receiver circuit, and to supply current from the drive control circuit to the differential receiver circuit.