Enhanced visible near-infrared photodiode and non-invasive physiological sensor
Embodiments of the present disclosure include a photodiode that can detect optical radiation at a broad range of wavelengths. The photodiode can be used as a detector of a non-invasive sensor, which can be used for measuring physiological parameters of a monitored patient. The photodiode can be part of an integrated semiconductor structure that generates a detector signal responsive to optical radiation at both visible and infrared wavelengths incident on the photodiode. The photodiode can include a layer that forms part of an external surface of the photodiode, which is disposed to receive the optical radiation incident on the photodiode and pass the optical radiation to one or more other layers of the photodiode.
1. A non-invasive physiological sensor which measures physiological parameters of a monitored patient, the sensor comprising:
an input configured to receive a drive signal from a driver circuit;
an emitter electrically coupled to the input and configured to emit optical radiation at one or more wavelengths responsive to the drive signal;
one or more detectors configured to be positioned proximate to the emitter and tissue of a patient by a sensor housing, the one or more detectors comprising one photodiode that is part of an integrated semiconductor structure, the one photodiode being configured to detect the optical radiation after attenuation by the tissue of the patient and generate a detector signal responsive to the detected optical radiation; and
an output electrically coupled to the one or more detectors and configured to output the detector signal,
wherein the one photodiode is configured to generate the detector signal with a signal strength sufficient for the detector signal to be usable to determine measurement values for one or more physiological parameters of the patient from the detected optical radiation at the wavelengths ranging from 450 nm to 1400 nm,
the one photodiode comprising a window layer, a diffusion region, an absorption region, and a semiconductor wafer, the absorption region being between the window layer and the semiconductor wafer, and
the window layer and the diffusion region are p-type regions, the window layer having a thickness ranging from about 25 nm to about 150 nm, the absorption region being an undoped region, the semiconductor wafer being a n-type region.
2. The sensor of claim 1 , wherein the thickness ranges from about 50 nm to about 100 nm.
3. The sensor of claim 1 , wherein the thickness is about 50 nm.
4. The sensor of claim 1 , wherein the window layer has a bandgap of about 1.52 eV at 25° C.
5. The sensor of claim 1 , wherein the window layer has a bandgap of about 1.68 eV at 25° C.
6. The sensor of claim 1 , wherein the window layer has a bandgap ranging from about 1.7 eV to about 1.9 eV at 25° C.
7. The sensor of claim 1 , wherein the absorption region comprises indium, gallium, and arsenic, and the window layer comprises indium, aluminum, and arsenic.
8. The sensor of claim 1 , wherein the absorption region comprises indium, gallium, and arsenic, and the window layer comprises indium and phosphorus.
9. The sensor of claim 1 , wherein the window layer is not lattice matched to the semiconductor wafer.
10. The sensor of claim 9 , wherein the window layer is not lattice matched to the absorption region.
11. The sensor of claim 1 , wherein the window layer is lattice matched to the semiconductor wafer.
12. The sensor of claim 1 , wherein the diffusion region is part of the window layer and the absorption region.
13. The sensor of claim 1 , wherein a first metal contact is adjacent to the semiconductor wafer, and a second metal contact is adjacent to the window layer.
14. The sensor of claim 1 , further comprising an anti-reflective coating on the one photodiode.
15. The sensor of claim 1 , further comprising a diffusion mask on the window layer, the diffusion mask comprising silicon.
16. The sensor of claim 1 , wherein the diffusion region is zinc-diffused.
17. The sensor of claim 1 , wherein the absorption region is adjacent to the semiconductor wafer.
18. The sensor of claim 1 , wherein the optical radiation contacts the window layer and the diffusion region prior to contacting the absorption region and the semiconductor wafer.
19. The sensor of claim 18 , wherein the optical radiation contacts the absorption region prior to contacting the semiconductor wafer.