Micro-sensor for detecting chemical species and associated manufacturing method
A microsensor for detecting ions in a fluid, comprises: a field-effect transistor having a source, a drain, an active region between the source and the drain, and a gate disposed above the active region, an active layer, in which the active region is formed, a dielectric layer positioned beneath the active layer, a support substrate disposed under the dielectric layer and comprising at least one buried cavity located plumb with the gate of the field-effect transistor in order to receive the fluid.
1. A microsensor for detecting ions in a fluid, comprising:
a field-effect transistor having a source, a drain, an active region between the source and the drain, and a gate positioned above the active region;
an active layer in which the active region is formed;
a dielectric layer positioned beneath the active layer; and
a support substrate positioned beneath the dielectric layer and comprising at least one buried cavity, located plumb with the gate of the field-effect transistor to receive the fluid, the at least one buried cavity comprising a constriction in a vicinity of the dielectric layer and a flared portion in a deeper zone of the support substrate.
2. The microsensor of claim 1 , wherein the at least one buried cavity is connected to a network of buried channels formed in the support substrate for transporting the fluid.
3. The microsensor of claim 2 , wherein the active layer has a thickness between a few nanometers and a few hundred nanometers.
4. The microsensor of claim 3 , wherein the dielectric layer has a thickness between a few ångströms and a few tens of nanometers.
5. The microsensor of claim 4 , wherein the active layer is formed of at least one semiconductor material selected from silicon, silicon-germanium, germanium, and III-V compounds (arsenides, phosphides, and nitrides).
6. The microsensor of claim 5 , wherein the dielectric layer comprises at least one insulating material selected from among silicon dioxide, silicon nitride, an oxynitride, hafnium oxide (HfO 2 ), alumina (Al 2 O 3 ), tantalum oxide (Ta 2 O 5 ) or a stack of layers of these materials.
7. The microsensor of claim 6 , wherein the active layer comprises silicon and the field-effect transistor has a fully depleted silicon-on-insulator (FDSOI) architecture.
8. The microsensor of claim 7 , wherein the at least one buried cavity has lateral dimensions of between around 100 nanometers and a few tens of microns and a depth of between a few tens of nanometers and a few hundred microns.
9. A process for fabricating a microsensor for detecting ions in a fluid, the process comprising:
providing a structure comprising an active layer positioned on a dielectric layer, the dielectric layer positioned on a support substrate, the structure comprising at least one buried cavity formed in the support substrate and positioned beneath the dielectric layer;
joining a first face of the support substrate to a first face of a donor substrate comprising the dielectric layer; and
producing a field-effect transistor having a source, a drain, an active region formed in the active layer and extending between the source and the drain, and a gate positioned above the active region, plumb with the at least one buried cavity.
10. The fabrication process of claim 9 , wherein providing the structure further comprises:
forming, on the first face of the support substrate, the at least one buried cavity by etching; and
thinning the donor substrate so as to form the active layer.
11. The fabrication process of claim 10 , wherein thinning the donor substrate comprises:
prior to joining, implanting light species in the donor substrate at the first face thereof to form a fragile buried layer; and
after joining, separating the donor substrate at the fragile buried layer to form the structure comprising the active layer positioned on the dielectric layer, the dielectric layer positioned on the support substrate, and a residual donor substrate.
12. The microsensor of claim 1 , wherein the active layer has a thickness between a few nanometers and a few hundred nanometers.
13. The microsensor of claim 1 , wherein the dielectric layer has a thickness between a few ångströms and a few tens of nanometers.
14. The microsensor of claim 1 , wherein the active layer is formed of at least one semiconductor material selected from silicon, silicon-germanium, germanium, and III-V compounds (arsenides, phosphides, and nitrides).
15. The microsensor of claim 1 , wherein the dielectric layer comprises at least one insulating material selected from among silicon dioxide, silicon nitride, an oxynitride, hafnium oxide (HfO 2 ), alumina (Al 2 O 3 ), tantalum oxide (Ta 2 O 5 ) or a stack of layers of these materials.
16. The microsensor of claim 1 , wherein the active layer comprises silicon and the field-effect transistor has an FDSOI architecture.
17. The microsensor of claim 1 , wherein the at least one buried cavity has lateral dimensions of between around 100 nanometers and a few tens of microns and a depth of between a few tens of nanometers and a few hundred microns.