Abstract
A radiation dosimeter comprising a thermal micro-platform with a plurality of nanowires having phononic structures providing improved thermal isolation of the micro-platform. In embodiments, thermo-luminescent, MOS transistor and PIN diode sensors for x-ray, gamma, charged particles and neutron irradiation are disposed on the micro-platform. In a preferred embodiment the dosimeter is fabricated using a silicon SOI starting wafer.
Claims
1. A radiation dosimeter comprising: a thermal micro-platform, the micro-platform having a support layer that is suspended by a plurality of nanowires at a perimeter thereof, and a device layer disposed on a portion of the support layer; an off-platform region, the off-platform region surrounding the micro-platform; wherein the plurality of nanowires comprised of a first layer having phononic scattering and/or phononic resonant structures physically configured to reduce thermal conductivity and wherein the micro-platform is comprised of a high energy sensor, a resistive heater and a temperature sensor.
2. The dosimeter of claim 1 wherein the high energy sensor is comprised of a first semiconductor device comprising one of a PN diode, PIN diode, or MOS transistor.
3. The dosimeter of claim 1 wherein the high energy sensor is comprised of a second thermo-luminescent device comprising a photonic emitter and with a semiconductor photodiode disposed nearby receiving photonic radiation from the thermo-luminescent emitter.
4. The dosimeter of claim 1 wherein the resistive heater is powered from an external power source providing an elevated temperature for one or more of readout with a thermo-luminescent sensor, reset of the sensor sensitivity and calibration of the sensor.
5. The dosimeter of claim 1 wherein the high energy sensor is comprised of a semiconductor device comprising one of a PN diode or a PIN diode having sensitivity to a transient dose high energy radiation.
6. The dosimeter of claim 1 wherein a portion of the resistive heater is a metallic film disposed on a nanowire providing an electrical connection of increased electrical conductivity.
7. The dosimeter of claim 1 wherein the temperature sensor is comprised of one or more of a thermistor, semiconductor diode or Peltier thermoelectric device.
8. The dosimeter of claim 1 wherein the resistive heater and temperature sensor provide a means of closed-loop temperature control when coupled with external control circuitry.
9. The dosimeter of claim 1 wherein the micro-platform and nanowires are at least partially formed from the device layer of a single semiconductor-on-insulator SOI starting wafer.
10. The dosimeter of claim 1 wherein the micro-platform is comprised of a semiconductor device layer having a diffused transistor.
11. The dosimeter of claim 1 further comprising semiconductor circuits are created in and on the surrounding support platform.
12. The dosimeter of claim 1 wherein the device layer is comprised of one of silicon, germanium, silicon-germanium, silicon carbide, and gallium nitride.
13. The device of claim 1 wherein the nanowire first layer has a phonon mean-free-path greater than the distance between the nanoscaled or atomic boundaries that comprise the phononic scattering and/or phononic resonant structures.
14. The device of claim 1 wherein the nanowire first layer has an electron mean-free-path less than the distance between the atomic- or nano-scale boundaries comprise the phononic scattering and/or phononic resonant structures.
15. The dosimeter of claim 1 wherein the plurality of nanowires is further comprised of a second layer comprising one of silicon nitride, silicon oxynitride, aluminum oxide, and silicon dioxide providing a reduction of stress across the micro-platform.
16. The micro-platform of claim 1 having a maximum structural dimension of less than 10 millimeters.
17. The dosimeter of claim 1 wherein the micro-platform is temperature-cycled between ambient temperature and temperatures up to 1000° C.
18. The device of claim 1 wherein the dosimeter is maintained under vacuum and a second heater is covered with a gettering material such as titanium particles which upon heating provides a means of degassing within the vacuum volume.
19. The dosimeter of claim 1 configured to further provide a wearable sensor interfaced with a mobile phone providing an assay and presentation of the sensor data.
20. The dosimeter of claim 1 configured to further provide a dosimeter within a wired or wireless sensor network.
Description
BRIEF DESCRIPTION OF THE FIGURES
(1) FIG. 1A is a plan view depicting a prior art micro-platform having supporting nanowires with an adaptation that reduces thermal conductivity.
(2) FIG. 1B is an illustrative view depicting a prior art nanowire adaptation that reduces thermal conductivity.
(3) FIG. 2 is a cross-sectional view depicting the prior art micro-platform of FIG. 1 formed by backside etching of a semiconductor handle wafer.
(4) FIG. 3 is a cross-sectional view depicting the prior art micro-platform of FIG. 1 formed by topside etching of a semiconductor handle wafer.
(5) FIG. 4A is a cross sectional view depicting the radiation dosimeter wherein the micro-platform is comprised of a thermo-luminescent structure sensitive to high energy radiation and adapted with a separate semiconductor pn diode photonic sensor in accordance with embodiments of the invention.
(6) FIG. 4B is a plan view depicting the dosimeter of FIG. 4A.
(7) FIG. 5A is a cross-sectional view depicting the radiation dosimeter wherein the micro-platform is comprised of a semiconductor PIN diode sensitive to high energy radiation dose in accordance with embodiments of the invention
(8) FIG. 5B is a plan view depicting a similar but slightly different embodiment of the dosimeter of FIG. 5A.
(9) FIG. 6A is a cross-sectional view of a radiation dosimeter wherein the micro-platform is comprised of a semiconductor MOST sensitive to high energy radiation in accordance with embodiments of the invention.
(10) FIG. 6B is a plan view depicting the dosimeter of FIG. 6A.
(11) FIG. 7 is a perspective view of a radiation dosimeter disposed on the backside of a mobile phone in accordance with embodiments of the invention.
DETAILED DESCRIPTION
Definitions
(12) The following terms are defined for use in this disclosure and the appended claims: “high energy radiation” means x-rays, gamma rays, charged particles, and neutrons originating from sources such as an x-ray tube, particle accelerator, and radioactive isotopes. Neutron energy range includes thermal neutrons. “micro-platform” means a platform having dimensions of about 100 nanometers on a side up to about 1 centimeter. “phononic structure” means a semiconductor structure adapted with phonon scattering or phonon resonating structures for the purpose of reducing thermal conductivity. “nano-dimensioned” or ‘nano-sized” means a structure whose largest dimension does not exceed 500 nanometers. “nano-wire” means a structure providing support for a micro-platform having nano-dimensioned thickness and width each with an arbitrarily long length. “sensor” means a device disposed in or on a micro-platform with sensitivity to high energy x-ray or nuclear radiation. “photonic sensor” means a pn diode sensitive to light in the visible and ultraviolet wavelength range.
(13) FIG. 4A is a cross-sectional view depicting the dosimeter in embodiment 400A wherein the high energy sensor is a TL structure bonded to the micro-platform. The micro-platform is comprised of a heater 402 and nanowires 214 with a supporting platform structure 346. Photonic radiation emitted from the TL structure 404 is detected by the semiconductor pn junction diode 406. The semiconductor diode is fabricated to be radiation hardened against the x-ray and/or nuclear radiation of interest as appropriate. This illustrative embodiment is fabricated from a starting silicon SOI wafer comprised a patterned silicon dioxide layer 344, handle substrate 342 and bonding film 354 with attachment to a header 352. The micro-platform and nanowires are released from the underlying support 342 with a backside DRIE, TMAH or RIE etch process. In addition in embodiments the silicon dioxide layer 344 may also be removed from the cavity area using a vapor HF process.
(14) FIG. 4B is a plan view depicting the structure of FIG. 4A wherein the TL structure 414 bonded to the micro-platform 412 is heated by resistive heater 402 with power supplied through pads 362 and 354 and nanowires 214. Supporting nanowires extend between the micro-platform 412 and surrounding support structure 410. The cavity 348 under the micro-platform 404 and nanowires 214 provides a further reduction in thermal conductivity between the support 410 and micro-platform 412. reduces the thermal nanowires 214 that are supplying power to the heater 402 generally are covered with a metal film of thin metal such as DC sputtered tungsten and lithographically patterned to provide a reduction in electrical resistance, especially for the resistive heater. In some embodiments a dielectric film such as silicon nitride, silicon oxynitride, or aluminum oxide is created between the metal film and the semiconductor portions of the nanowire with appropriate lithographic patterning. In some embodiments a CVD dielectric film such as silicon nitride or silicon oxynitride is patterned over the nanowires to provide a reduction of stress across the micro-platform.
(15) FIG. 5A is a cross-sectional view depicting the dosimeter adapted with a semiconductor PIN diode 502 as the high energy sensor. The sensor is disposed on the micro-platform 110 and connected to external circuitry via bonding wires 504 and 506. In this depicted embodiment the contacting metallic wires to the PIN diode 502 overlay the electrical connections to the heater on the phononic first layer of a nanowire 214. The upper cavity boundary structural area 108 is comprised of the micro-platform 110 and nanowires 214. The active layer 346, silicon oxide 344, and handle support 342 of the starting silicon wafer 340 enclose the patterned cavity 125. The film 354 bonds the patterned handle wafer 342 to the header 352
(16) FIG. 5B is a plan view depicting a dosimeter adapted with a semiconductor PIN diode 502 as shown in the schematic 504 where the electrical connections 507 and 508 to the PN diode are routed over nanowires separate the heater nanowires 362 and 364. The micro-platform 412 is suspended via nanowires connected to the surrounding support platform 408 and suspended over cavity 125. Generally the nanowires supplying power to the heater are covered with a nanolayer of high temperature metal such as tungsten. In some embodiments the surrounding support platform electrical resistivity is so large that an insulating dielectric film is not needed to insulate the heater wire from parasitic electrical shunt conduction through the supporting platform 408. At least one of the connection traces to the PIN diode is insulated from the device layer by a patterned overlying tungsten film.
(17) In embodiments, the PIN diode may be connected to a transimpedance amplifier to provide nanosecond response to prompt radiation. This feature is helpful, for ample, for follow-up monitoring after the alert indicating a high-dose is registered.
(18) FIG. 6A is a cross-sectional view of a dosimeter adapted to provide a MOST high energy sensor. In this embodiment the MOST is diode-connected 504 with the gate shorted to the drain. Wire 606 connects to the drain-gate and wire 608 connects to the transistor source. The micro-platform 110 area comprises the MOST and its two electrical connections The suspended structural area 108 is comprised of the micro-platform 110 and the nano-wires. The nanowire depicted provides a support for the metal connection with the MOST and the insulating film 356. The stacked components of the SOI starting wafer 340 include the device layer 346, the silicon dioxide layer 344, the handle wafer 342. The handle wafer 342 is bonded to the header 352 via bonding film layer 354. The surrounding support platform is 214 provide connection to the heater in this embodiment. The drain of the MOST surrounds the source and provides a guard ring against surface leakage. Incident radiation deposits energy into the gate dielectric of the MOST transistor causing a shift in threshold voltage V.sub.T.
(19) FIG. 6B is a plan view depicting the dosimeter of FIG. 6A adapted with a MOST sensor. The wired bonding pad connections 606 and 608 to the MOST are disposed on the surrounding support platform 408 The MOST connections are made through nanowires separate from the heater connections. A first heater is connected through pads 610 and 612 and another heater is connected to external power through pads 614 and 616. Both electrically conducting and non-conducting nanowires support the micro-platform 412 and are tethered to the surrounding support platform 408 at periphery 410.
(20) FIG. 7 is a perspective view of the dosimeter adapted with support circuitry as a clip-on to the backside of a mobile phone 710. In this embodiment the dosimeter is adapted with additional circuitry as module 720. The dosimeter function is powered from and communicates with the mobile phone through the standard micro-USB bus 730. In embodiments alerts are communicated when the radiation dose level exceeds a predetermined level or levels.
(21) It is to be understood that although the disclosure teaches many examples of embodiments in accordance with the present teachings, many additional variations of the invention can easily be devised by those skilled in the art after reading this disclosure. As a consequence, the scope of the present invention is to be determined by the following claims.
